Take a look at the passage again:
Peering around the other students in line, Sylvia tried to see the lunch
choices. The cafeteria selections were disappointing.
For example, greasy fried chicken, soupy sweet-n-sour pork, and a gray mystery
meat floating in translucent, lumpy gravy.
You chose the second part, The cafeteria selections were disappointing. This part has a main clause: selections is the subject; were is the verb. A fragment will not have a main clause.
Go back to the passage to try again.