Take a look at the passage again:
Phillip left work early. To memorize the vocabulary that his Spanish midterm
would test the next day. But all that he could
think about was Beatrice, the cute new sales associate who worked in the
camera department.
You chose the third part, But all that he could think about was Beatrice, the cute new sales associate who worked in the camera department. This part has a main clause: All is the subject; was is the verb. A fragment will not have a main clause.
Go back to the passage to try again.