Question

which sentence uses the passive voice for the main verb?
if we use our cell phones during class, the teacher confiscates them.
when they can, students slide down the banister in the science wing.
when we can pick our reading, mythology is most often chosen in my class.
if they choose to participate, students perform their poems at the poetry slam.

Explanation:

In passive - voice sentences, the subject receives the action of the verb. In "When we can pick our reading, mythology is most often chosen in my class", "mythology" is the subject and it is being chosen (receiving the action), while in the other sentences the subjects are performing the actions.

Answer:

When we can pick our reading, mythology is most often chosen in my class.