Question

Well, you _____________ fit everything in a backpack so you must be selective.
(A) might not
(B) cannot
(C) mustn’t
(D) should not

Answer 1

Hint: Words like ‘might’, ‘may’, ‘should’, ‘can’etc. are examples of auxiliary verbs.Auxiliary verbs are used with another verb in order to show the tense of existing sentence or to make an interrogative statement. They can be even transferred to modal verbs which are used to explain ideas such as possibility, necessity and permission.

Complete step by step answer:
1. In order to find out the correct option which would fit in the sentence, we need to find out the usage of the given options.
2. The first option is 'might not'. As we know the word 'might' is used when we have a choice to go either way. But here in this sentence, it is specified that there is no other way, she cannot be selective in any case. Therefore, 'might not' can’t be the correct option.
3. The third option is 'mustn't'. The word ‘must not’ (the contracted form is ‘mustn’t’) is used to mean one should not do that work in any circumstances. Here, in the context of this question, there is no such option of being selective. So, if we don’t have any such option of being selective then there is no point in using this word. Therefore, this option is also incorrect.
4. In the fourth option, the word 'should not' is used. Here again, she does not have an option of being selective, so it is wrong to use 'should' or 'should not' in this perspective. Therefore, this option is proved as also inappropriate.
5. The second option, that is, 'cannot' suits right in that scenario. She 'cannot' choose to be selective.

Hence the option B is the right answer.

Note:
These auxiliary verbs are used in different forms and in different perspectives. We can change the nature of the sentence just by changing these verbs. Hence, it is important to use these words carefully in order to convey the real perspective of the sentence.