Question

Fill in the blank with the suitable modal:
I _______ swim when I was three.
A) Could
B) Can
C) Have to
D) Must

Answer 1

Hint: Modal is a type of verb that is used to indicate modality. Modal verbs always accompany the base form of another verb having semantic content.

Complete step by step answer:
Option A) Could – is the correct answer because ‘could’ is used to express an ability or a lack of an ability or make a polite request or make a suggestion or to express a specific possibility or make a negative deduction. "Could" is used in past tense because the sentence was in past tense. Thus, this is the correct answer.
Option B) Can – is an incorrect answer because ‘can’ is used to express an ability or lack of an ability or to give permission or express a prohibition or to make an informal request or to express a general possibility or to make a negative deduction. “Can" is used in Present & Future tense not in past tense. So, this is an incorrect answer.
Option C) Have to – is an incorrect answer because ‘have to’ is used to express an external obligation in positive sentences and removing an external obligation in the negative sentences. So, the use of have to is the most inappropriate in the blank. So, this is an incorrect answer.
Option D) Must – is an incorrect answer because ‘must’ is used to express a necessity (in the present or future) or to make an assumption that something is true. Thus, must cannot be used here in the blank as it does not give any sense in the sentence. So, this is an incorrect answer.

So, the correct answer is “Option A”.

Note:
Here in the question, we see that the speaker is expressing his or her ability to swim when he or she was three years old. As the sentence is in Past Tense, "can" is inappropriate. "Have to" is not used to express an ability, thus it is also inappropriate. "Must" is also not used to express an ability, thus it also is inappropriate. Therefore, from among the options, 'could' is the most suitable verb to complete the sentence. Thus, the correct complete sentence is: I could swim when I was three.