Modal Verbs

Respuesta correcta: A) might

• A) mightCorrect. 'Might' expresses a possibility in the present or future without committing either way.
• B) shallWrong. 'Shall' is used mainly in offers and suggestions, which is not the meaning required here.
• C) can'tWrong. 'Can't' expresses prohibition or impossibility, the opposite of an open possibility.
• D) mustWrong. 'Must' expresses strong obligation or logical certainty, which contradicts the uncertainty described.

Respuesta correcta: B) You must wear a helmet when you ride a motorcycle.

• A) You might wear a helmet when you ride a motorcycle.Wrong. 'Might' expresses possibility, which is entirely wrong for a safety rule.
• B) You must wear a helmet when you ride a motorcycle.Correct. 'Must' expresses a strong external obligation imposed by a rule or law.
• C) You would wear a helmet when you ride a motorcycle.Wrong. 'Would' is the conditional form and does not convey obligation in this context.
• D) You should wear a helmet when you ride a motorcycle.Wrong. 'Should' expresses advice or recommendation rather than a binding requirement.

Respuesta correcta: C) You should see a doctor before it gets worse.

• A) You can see a doctor before it gets worse.Wrong. 'Can' expresses ability or permission, which is unrelated to medical advice.
• B) You must see a doctor before it gets worse.Wrong. 'Must' turns advice into a binding requirement, which changes the relationship between the speakers.
• C) You should see a doctor before it gets worse.Correct. 'Should' expresses personal advice or recommendation and leaves the final decision to the listener.
• D) You might see a doctor before it gets worse.Wrong. 'Might' expresses the possibility of an action, not a recommendation to perform it.

Respuesta correcta: D) You mustn't use your phone during the exam.

• A) You shouldn't use your phone during the exam.Wrong. 'Shouldn't' is advice not to do something, which is weaker than a prohibition.
• B) You needn't use your phone during the exam.Wrong. 'Needn't' also removes an obligation rather than forbidding an action.
• C) You don't have to use your phone during the exam.Wrong. 'Don't have to' removes an obligation, which is the opposite of prohibition.
• D) You mustn't use your phone during the exam.Correct. 'Mustn't' expresses prohibition, telling the student that using the phone is forbidden.

Respuesta correcta: A) That can't be right; the data clearly show the opposite.

• A) That can't be right; the data clearly show the opposite.Correct. 'Can't' conveys a confident rejection of the statement, which matches the evidence cited.
• B) That needn't be right; the data clearly show the opposite.Wrong. 'Needn't' removes an obligation and has no bearing on whether a statement is true.
• C) That may not be right; the data clearly show the opposite.Wrong. 'May not' is a weaker and more hedged rejection than the confident 'can't' in this context.
• D) That might be right; the data clearly show the opposite.Wrong. 'Might be right' expresses possibility and contradicts the certainty in the second clause.

Respuesta correcta: B) must have been

• A) must beWrong. 'Must be' expresses certainty about the present, not about a past situation.
• B) must have beenCorrect. 'Must have been' expresses a deduction in the past based on present evidence.
• C) must to beWrong. 'Must to be' inserts an infinitive marker that modal auxiliaries do not take.
• D) must beenWrong. 'Must been' lacks the participle that the perfect form requires.

Respuesta correcta: C) Must presents the obligation as external and unavoidable, while should presents it as the speaker's personal recommendation.

• A) Must is used only for the past and should is used only for the future.Wrong. Both modals are used in the present and in the past with perfect forms; neither is restricted to one time.
• B) Must and should are exactly synonymous in every context and can be interchanged freely.Wrong. The two modals differ in strength and in the origin of the obligation, so they are not freely interchangeable.
• C) Must presents the obligation as external and unavoidable, while should presents it as the speaker's personal recommendation.Correct. This captures the conventional distinction between externally imposed obligation and personal recommendation.
• D) Should is stronger than must because it leaves no room for personal judgement.Wrong. Should is weaker precisely because it leaves the decision to the listener.

Respuesta correcta: D) He can't have finished the report; the office is still lit and he's still working.

• A) He mustn't have finished the report; the office is still lit and he's still working.Wrong. 'Mustn't have' expresses prohibition rather than a deduction about a past event.
• B) He may have finished the report; the office is still lit and he's still working.Wrong. 'May have' is a possible deduction but it is weaker than the certainty expressed by the evidence.
• C) He might have finished the report; the office is still lit and he's still working.Wrong. 'Might have' leaves the question open and contradicts the confident reasoning in the second clause.
• D) He can't have finished the report; the office is still lit and he's still working.Correct. 'Can't have' plus participle expresses certainty that a past action did not happen, which the evidence supports.

Respuesta correcta: A) You don't have to pay a deposit if you bring your own tent.

• A) You don't have to pay a deposit if you bring your own tent.Correct. 'Don't have to' states that an obligation does not exist, which is different from forbidding the action.
• B) You shouldn't pay a deposit if you bring your own tent.Wrong. 'Shouldn't' advises against paying, which is not the same as saying payment is unnecessary.
• C) You can't pay a deposit if you bring your own tent.Wrong. 'Can't' expresses inability or impossibility, neither of which is meant here.
• D) You mustn't pay a deposit if you bring your own tent.Wrong. 'Mustn't' prohibits the deposit, which is the opposite of what the sentence intends to convey.

Respuesta correcta: B) had studied

• A) studiedWrong. 'Studied' with 'if only' is not the standard form for an unreal past condition.
• B) had studiedCorrect. 'Had studied' forms the third conditional with 'would have passed', expressing an unreal situation in the past.
• C) would studyWrong. 'Would study' belongs to an unreal present condition and does not match the 'would have passed' clause.
• D) have studiedWrong. 'Have studied' is the present perfect and does not create an unreal past condition.

Respuesta correcta: C) Visitors had to register at the gate before the new system was introduced.

• A) Visitors must register at the gate before the new system was introduced.Wrong. 'Must' likewise states a present obligation rather than a past one.
• B) Visitors have to register at the gate before the new system was introduced.Wrong. 'Have to' states a present obligation, which contradicts the reference to a superseded system.
• C) Visitors had to register at the gate before the new system was introduced.Correct. 'Had to' refers to an obligation that applied in the past and no longer applies.
• D) Visitors had better register at the gate before the new system was introduced.Wrong. 'Had better' is an advisory expression and does not describe an obligation that has ended.

Respuesta correcta: D) The samples could have been contaminated during transport.

• A) The samples may have contaminated during transport.Wrong. 'May have contaminated' uses the wrong participle and describes the samples as the agents of the action.
• B) The samples can't have been contaminated during transport.Wrong. 'Can't have' confidently denies the contamination, which is a stronger claim than caution allows.
• C) The samples must have been contaminated during transport.Wrong. 'Must have' asserts the contamination as certain, which is the opposite of caution.
• D) The samples could have been contaminated during transport.Correct. 'Could have' plus participle is the most tentative of these options and fits the cautious register of the letter.

Respuesta correcta: A) You should see a specialist; if you leave it too long, it gets much harder to treat.

• A) You should see a specialist; if you leave it too long, it gets much harder to treat.Correct. 'Should' gives advice without compelling, and the conditional clause warns about delay.
• B) You could see a specialist; if you leave it too long, it gets much harder to treat.Wrong. 'Could' expresses possibility or permission here and does not function as advice.
• C) You might see a specialist; if you leave it too long, it gets much harder to treat.Wrong. 'Might' expresses possibility of the action and gives the listener no recommendation at all.
• D) You must see a specialist; if you leave it too long, it gets much harder to treat.Wrong. 'Must' compels rather than advises, which removes the speaker's own nuance from the message.

Respuesta correcta: B) They didn't have to attend the briefing, which was optional that year.

• A) They mustn't have attended the briefing, which was optional that year.Wrong. 'Mustn't have' states that attending was forbidden, which contradicts the fact that it was optional.
• B) They didn't have to attend the briefing, which was optional that year.Correct. 'Didn't have to' is the past form of the absence of an obligation, which matches the note that it was optional.
• C) They can't have attended the briefing, which was optional that year.Wrong. 'Can't have' denies the attendance entirely, which is a different claim from saying it was not required.
• D) They didn't need to have attended the briefing, which was optional that year.Wrong. 'Didn't need to have' mixes two structures and adds an unnecessary perfect to the requirement.

Respuesta correcta: C) The committee could extend the deadline if the funding is approved on time.

• A) The committee would extend the deadline if the funding is approved on time.Wrong. 'Would extend' describes a hypothetical outcome rather than a possibility open to decision.
• B) The committee must extend the deadline if the funding is approved on time.Wrong. 'Must' asserts that the extension is inevitable, which the condition does not guarantee.
• C) The committee could extend the deadline if the funding is approved on time.Correct. 'Could' expresses a real possibility in a conditional context without asserting that it will happen.
• D) The committee shall extend the deadline if the funding is approved on time.Wrong. 'Shall' is used for formal offers and suggestions, not for expressing possibility.

Respuesta correcta: D) The author presents the effect as genuinely possible without committing to it.

• A) The author denies that the policy could have any effect on emissions.Wrong. Denial would require cannot or mustn't, so the sentence does not take the meaning attributed to it.
• B) The author states that the policy is obliged to reduce emissions by law.Wrong. Obligation would be expressed with must or shall, neither of which appears in the sentence.
• C) The author asserts that the policy will certainly reduce emissions.Wrong. 'Certainly' would require a stronger modal such as must or will, and that is not what the sentence says.
• D) The author presents the effect as genuinely possible without committing to it.Correct. Could is the modal of possibility, so it presents the outcome as feasible without guaranteeing it.

Respuesta correcta: A) You had better check the contract before you sign it.

• A) You had better check the contract before you sign it.Correct. 'Had better' conveys a strong recommendation without removing the listener's freedom to act differently.
• B) You might check the contract before you sign it.Wrong. 'Might' is too weak for a situation in which serious consequences are at stake.
• C) You could check the contract before you sign it.Wrong. 'Could' and 'might' both present the action as merely possible, which is far weaker than a strong warning.
• D) You must check the contract before you sign it.Wrong. 'Must' imposes an obligation and eliminates any choice on the client's part.

Respuesta correcta: B) She can't have left without her keys, and she must have locked the door behind her.

• A) She can't have left without her keys, and she must have lock the door behind her.Wrong. 'Must have lock' lacks the past participle after the auxiliary 'have'.
• B) She can't have left without her keys, and she must have locked the door behind her.Correct. Both clauses use the modal plus perfect pattern with the correct past participle, and both express confident deduction.
• C) She can't have left without her keys, and she must locked the door behind her.Wrong. 'Must locked' places a past form directly after the modal, omitting the auxiliary that carries the perfect.
• D) She can't have left without her keys, and she must has locked the door behind her.Wrong. 'Must has' combines a modal with a present form of the auxiliary, which is not valid.

Respuesta correcta: C) We would prefer an answer by Friday, though we recognise your schedule may not allow it.

• A) We shall receive an answer by Friday, though we recognise your schedule may not allow it.Wrong. 'Shall' is used for official announcements rather than for a negotiator's own preference.
• B) We must have an answer by Friday, though we recognise your schedule may not allow it.Wrong. 'Must have an answer' makes the deadline a requirement and contradicts the concession in the second clause.
• C) We would prefer an answer by Friday, though we recognise your schedule may not allow it.Correct. 'Would prefer' registers a strong preference without turning it into an obligation, which is tactful in a negotiation.
• D) We can have an answer by Friday, though we recognise your schedule may not allow it.Wrong. 'Can' expresses the possibility of receiving an answer, which conveys no pressure at all.

Respuesta correcta: D) Under the old policy, staff were required to submit timesheets every Friday.

• A) Under the old policy, staff must have submit timesheets every Friday.Wrong. 'Must have submit' lacks the past participle after the auxiliary 'have'.
• B) Under the old policy, staff are required submitting timesheets every Friday.Wrong. 'Are required submitting' mixes present passive with a gerund and does not locate the rule in the past.
• C) Under the old policy, staff must to submit timesheets every Friday.Wrong. 'Must to submit' cannot follow a modal, and the sentence also lacks any reference to the past.
• D) Under the old policy, staff were required to submit timesheets every Friday.Correct. 'Were required' is the past passive form of a rule that applied in that period and no longer does.