Chhaya is not known . . . . . . . . me. A. to B. on C. at D. with

The correct answer is A. to.

The preposition “to” is used to indicate a relationship between two people or things. In this case, Chhaya is not known to me, meaning that I do not know her.

The other options are incorrect because they do not indicate a relationship between two people or things. The preposition “on” is used to indicate a location or position. The preposition “at” is used to indicate a time or place. The preposition “with” is used to indicate a relationship between two people or things, but it is typically used

In conclusion, the correct answer is A. to.