Question

Fill in the blank with a suitable modal auxiliary:
I_______ that coat if I were you.
A. mustn't buy
B. Won’t buy
C. wouldn't buy
D. can't buy

Answer 1

Hint: An auxiliary verb is a verb in which the clause in which it occurs adds functional or grammatical meaning in order to express tense, aspect, modality, voice, focus, etc. Usually, auxiliary verbs are preceded by an infinitive verb or a participle that provides the key semantic substance of the clause.

Complete answer:
Modal Verbs inform us the speaker 's attitude about what is being said or done. The word "modal" suggests that expressing emotion and mood is a way of expressing the speaker’s attitude.
Option C is the correct answer since it communicates confusion and it encourages the mood of something that has not occurred in the past according to the given expression.
Whereas, option A expresses assurance as to whether the act is not performed;
Option B expresses certainty that it will not be purchased in the future.
Inability is represented by option D. Therefore, these three alternatives do not fit into the question

Hence the correct answer is option ‘C’

Note: To answer this type of question you need to develop the basic understanding about the common modal verbs. Here is a list of modal verbs:
Can, could, may, might, will, would, shall, should, must
The verbs or expressions dare, ought to, had better, and need not behave like modal auxiliaries to a large extent and may be added to the above list given.