Grandmother is sitting . . . . . . . . the fire. A. on B. with C. by D. in

The correct answer is C. by.

Grandmother is sitting by the fire because she is enjoying the warmth. She may also be sitting by the fire to read, to knit, or to talk to someone.

The other options are not as likely. Grandmother is not sitting on the fire because that would be dangerous. She is not sitting with the fire because that would mean that