Fill up the blank, with the correct option
My father is……………... sixty.

Correct option is C

The correct answer is (c) of.

My father is of sixty.

In English, when we talk about a person's age using "is," we generally use the preposition "of" to indicate age in some formal or literary contexts. The phrase "of sixty" means "having the age of sixty."

Why other options are incorrect:

(a) on → "On sixty" is incorrect because "on" is generally used for specific days or surfaces (e.g., "on Monday," "on the table").

(b) below → "Below sixty" means "less than sixty," but the sentence does not indicate a comparison. It just states the father's exact age.

(d) after → "After sixty" means "older than sixty," which changes the meaning of the sentence.

Thus, the correct answer is (c) of.