Question

Which words in the sentence are the complete adjective clause? At the orchestra concert, my sister, who plays the flute, held a note for a long time. A. held a note for a long time B. for a long time C. who plays the flute D. at the orchestra concert\

Answer 1

your answer would be c who  plays the flute

Answer 2

At the orchestra concert, my sister, who plays the flute, held a note for a long time.
This is who plays the flue because it is a adverb clause.
"Plays the flute"
and "who"
make it a adverb clause.