Question

Fill a suitable option as per the situation given:
(The doorbell rings) I wonder who that is. It ________ Mary. She's still at work at this time.
A) couldn't be
B) can't be
C) won't be
D) mustn't be

Answer 1

Hint: This question is about Modal Verbs. Modal verbs are used to express the attitude of the speaker in regard to what is being said. “Modal” means the mood of the speaker. While working with modal verbs, keep in mind the subject and the sense of the sentence. There are many different types of Modal verbs, each with its own specific usage. Remember this while working with these types of questions.

Complete answer:
The given question is a premise where the subject hears the doorbell and starts to imagine who it can be. He, later on, reaches a conclusion that Mary cannot be the person at the door as she is at work. Knowing this information, we can say that the required modal verb here must relate to the capability of Mary.

Let us analyze the given options:
Option (A) couldn't be: Option A is incorrect because it expresses the inability of Mary to be at the door but in the past tense while the sentence is in the present tense.
Option (B) can't be: Option B is correct because it properly expresses the inability of Mary to be at the door in the present tense.
Option (C) won't be: Option C is incorrect because it is in the future tense but the sentence is in the present tense.
Option (D) mustn't be: Option D is incorrect because it is somewhat forcing the inability as an obligation, not an ability.

Therefore the correct answer is option ‘B’.

Note: Basic rules of modal verbs:
- Use the modal verb as is. Don't change its form and turn it into the present, future, or past forms.
- Use the base form of the verb after a modal. Don't use “to” or the full infinitive verb “to”. ...
- If you need to use models in the negative form, then use only “not” AFTER the modal verb.