Answer:
I believe the answer is the first one, clases-llenas.
Explanation:
Clases is a feminine word (las clases, la clase), so it only makes sense for the adjective after it to be feminine as well (llenas). Please let me know if you still need help with this, and only mark as brainliest if you want!
The answer is (al) becuase they listen to the professor
It is most likely B) el ensayo. A practice before a peformance.