Answer: They draw the audience's eye away from the foreground
Explanation:
backgrounds are not necessarily darker than the subject! so this cannot be the answer choice.
competing elements MAY be the answer because this sounds plausible. but then again a background could just be one color.
a main issue is drawing the audience's eye away from the foreground (otherwise called the subject). FOV could help with this so that the bg is blurred.
the fourth one makes no sense since its all within one digital file
