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, the subject receives the action. Here, "mythology" (subject) receives the action "chosen". Other sentences have subjects performing actions (e.g., "teacher confiscates", "students slide", "students perform") which are active voice.

Answer:

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