Take a look at the sentence again:
Belinda saw very little of the horror movie, for she shut her eyes __________,
when she heard the monster's footsteps in the dead leaves, and when characters
started screaming.
The blank requires a subordinate clause. You chose during the violin music, which is a prepositional phrase and thus causes a parallelism error. Before you continue, review the rules for parallel structure.
Go back to the sentence to try again.