Question

You ___________ get the 8.45 train. It doesn’t stop at Yorkshire.
A. Had better
B. Mustn’t
C. Should
D. Don’t have to

Answer 1

Hint:
Mustn’t is used to talk about something which is debarred, or to stop someone from doing something. We use this to talk about things that we need to avoid or things that are not to be done. We use mustn’t particularly when the prohibition comes from the speaker.

Complete answer:
Option A: Had better is used to refer to an action that is desirable, or to give advice in a particular situation, especially when you want to ensure you avoid a negative consequence outcome. Thus, the option ‘a’ is not correct.
Option B: Mustn’t is basically used to stop someone from doing a particular thing. In this given sentence, the speaker wished to stop the person from getting the 8.45 train because it will not take him to his desired destination. Mustn’t is an obligation not to do a particular thing or something. Thus, option ‘b’ is absolutely correct.
Option C: Should is a modal verb and is used to make recommendations or give advice. It can also be used to express some duty or say some obligation or to make recommendations or give advice. Thus, the option ‘c’ is absolutely incorrect.
Option D: Don’t have to is used to refer to an option action or to say that there is no obligation or necessity to do something. Thus, option ‘d’ is not correct.

Note:
Mustn’t is used to say when something is not allowed or in case something is prohibited. When you want to say it is necessary that you do not do something, then use mustn’t. We use this to talk about things that we need to avoid or things that are not to be done.