Question

Fill in the blank with a suitable modal:
Our train leaves in two minutes! We _______ hurry.

• A. would
• B. have to
• C. must
• D. don't have to

Answer 1

Answer: (C)

must

Answer : C

Modal verbs are auxiliary verbs that are used to express necessity or possibility.

Let's take a look at the usage of the modal verbs in the options:

• would : It is used to make either a polite request or make a polite expression; also it is used to refer to a habitual action in the past
  
• have to : It is used to express an external obligation in positive sentences and removing an external obligation (or necessity) in the negative sentences
  
• must : to express a necessity (in the present or future); to make an assumption that something is true
  
• don't have to : It is the negative form of 'have to

Here in the question, we see that the speaker is expressing the necessity, that is to hurry up or they would miss their train.

• As it is not a request or a polite expression -- 'would' is not suitable.
• Also, the sentence is not in the negative form -- 'don't have to' -- is not suitable; it is used to remove a necessity to express one.

Now the tricky part is to choose between 'must' & 'have to', both apparently seems appropriate for use here in the sentence.

The main difference between 'must' & 'have to' is that 'must' is a necessity felt by the speaker whereas 'have to' is an external obligation or rule. If this distinction is not important, you can use 'must' and 'have to' interchangeable in positive sentences.

But here the train would leave whether or not the speaker arrives on time, right, therefore it is NOT an external obligation but the necessity felt by the speaker and thus here 'must' is the most suitable verb to complete the sentence.

Thus, the correct complete sentence is:

Our train leaves in two minutes! We MUST hurry.