Which sentence contains a gerund phrase?

A. Practicing the piano daily has helped Maria master Beethoven's "Moonlight Sonata."

B. "Moonlight Sonata" has been performed more than 10,000 times.

C. Tran urges us to be quiet because, as Maria plays, he is listening.

D. After he wrote "Moonlight Sonata," Beethoven felt the result was satisfying.