First off, for ".mp3" files, if the choices are:
a. audio
b. video
c. document
d. compressed
Then it's (a) audio files. If it were ".mp4", then it would be a video file.
Second, for ".zip" files, if the choices are:
a. graphic
b. audio
c. compressed
d. document
Then it's (c) compressed files. Compressed files are also known as zipped folders. This keeps the files from being edited or deleted. This file extension is where the "zipped folder" term comes from.
Hope that helps!