Which one of the following groups of words is a fragment?

A. Strolling in the park on a summer afternoon.

B. In December, we usually take a skiing trip.

C. Talking on the phone is her favorite pastime.

D. The Carters enjoy vacationing at the lake.

The statement in option A is a fragment. This is because the statement does not express a complete sense. A complete sentence must have at least one independent clause which is made up of a subject and a verb and the sentence must be able to stand on its own.