Take a look at the passage again:
Emily pounded on the bedroom door, demanding a little quiet so that she
could study for her physics midterm. Her sister
Amy ignored the request. And continued banging on the drum set that
she bought at a garage sale.
You chose the second part, Her sister Amy ignored the request. This part has a main clause: sister is the subject; ignored is the verb. A fragment will not have a main clause.
Go back to the passage to try again.