Question

Fill in the blank with the most appropriate option:
Why didn’t you help him? You ___ have done it.
A) must
B) can
C) could
D) were to

Answer 1

Hint: In the given question, we have to complete the sentence choosing the appropriate modal verb. The given sentence is in simple past tense because the word “didn’t” is used. Hence, we have to use the past tense of appropriate modal verbs.

Complete answer:
A modal verb is a type of verb that is used to indicate modality – that is: likelihood, ability, permission, request, capacity, suggestions, order, obligation, or advice. In English, the modal verbs commonly used are can, could, must, should, had better, have to and sometimes need or dare.

Let us evaluate the options:
Option A) must – This option is incorrect because the word “must” is used to give command or order. Here the speaker is not commanding rather he is asking for the reason of not helping. Hence, it is not appropriate to use the word “must”.
Option B) can – This option is incorrect because the sentence is in past tense. We cannot use the present form “can” for continuing the past tense sentence “why didn’t you help him?”
Option C) could – This option is correct because “could” is the past form of “can”. The speaker is conveying that the other person could’ve helped but didn’t do it so. Since the first sentence is in past tense, the word “could” in the second sentence is the appropriate answer.
Option D) were to – This option is incorrect because “were” is past tense of auxiliary verbs “are”. We have to use a modal verb as an appropriate answer. “Were” is not a modal verb and cannot be used together with the second person singular “You” in the given sentence. Moreover, “have” has been already used in the sentence so we cannot use “to” together with “were”.

Hence option C is correct. Why didn’t you help him? You could have done it. – is the correct answer.

Note: We have to pay attention to the tense of the sentence and the action that takes place in the sentence. In the given question, the action (chance) of “not helping” was already over hence the answer should be in past tense.