Take a look at the passage again:
Head down, Lela stared at the textbook on her desk.
She understood the fragment practice that Mrs. Markham was going over in
class. But was too shy to raise her hand and volunteer an answer.
You chose the first part, Head down, Lela stared at the textbook on her desk. This part has a main clause: Lela is the subject; stared is the verb. A fragment will not have a main clause.
Go back to the passage to try again.