The answer is notice key words and details.
A.I'm not satisfied with your explanation of where you <u>were</u> last night.
b.I came into the room when Mary <u>was playing</u> the piano.
c.no error!!!
d.There <u>are</u> some sheep in the field.
e.Playing the drums and singing<u> is </u>difficult.
The correct answer is letter A. To answer your <span>question, I must first fill you in on the background.</span><span> The phrase fragments are already completely filled with the idea. It is not alone a fragment where no idea nor thought that is being presented compared to a complete sentence.</span>