Correct option is A
The correct preposition to fill in the blank is “of.”
Explanation:
The correct phrase is "afraid of," which is used to indicate fear or apprehension about something.
Example of correct answer in a sentence: Are you afraid of the dark?
Meanings of other options:
At: Used to indicate a location or specific time.
On: Used to indicate a surface or day.
To: Used to indicate direction or purpose.