Fill in the blank with suitable modal from the options below:
"Who is she? She ______ be his sister".
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → must
Complete sentence: "Who is she? She must be his sister." The speaker does not know who the woman is ("Who is she?") and, from what he sees, draws the firm conclusion that she must be his sister.
| Option | Meaning and use | Example |
|---|---|---|
| (1) must (answer) | Besides duty, must expresses a strong deduction: the speaker is almost sure that something is true from what he sees or knows. | The lights are off; they must be asleep. |
| (2) should | Should expresses advice, duty or what is expected to happen. It does not draw a conclusion about who someone is. | You should drink more water in summer. |
| (3) would | Would is used mainly for conditions, polite requests and past habits. It does not express the firm conclusion the speaker draws here. | If I had wings, I would fly to you. |
| (4) need | As a modal, need expresses necessity and is used mainly in negatives and questions. It cannot express a guess. | You need not wait for me. |