Take a look at the passage again:
Jonathon often tries to shock his English teacher, Mrs. Mauzy, with weird
paper topics. Such as eating tarantulas or wearing women's underwear.
Mrs. Mauzy remains nonplussed, scandalized only
by the number of fragments in Jonathon's essays.
You chose the third part, Mrs. Mauzy remains nonplussed.... This part has a main clause: Mrs. Mauzy is the subject; remains is the verb. A fragment will not have a main clause.
Go back to the passage to try again.