Take a look at the passage again:
Dr. Gregory surveyed the auditorium full of nervous,
sweating biochemistry students. Her gaze often stopped on Bryan.
Whose test anxiety manifested in the loud popping of his knuckles and the
high-speed bouncing of his left leg.
You chose the first part, Dr. Gregory surveyed the auditorium full of nervous, sweating biochemistry students. This part has a main clause: Dr. Gregory is the subject; surveyed is the verb. A fragment will not have a main clause.
Go back to the passage to try again.