What is the error on the subject-verb agreement?

modern calculators, which can compute sums almost instantaneously, derives from abacuses, hand operated devices with beads that slide along rods.

Why is it important to be aware of you audience's interests? a. so that you can teach them new information thy didn't know b. so that you can use opposite ideas in order to shock them c. so that you can use the most effective strategy to persuade them d. so that you can pretend to like the same things and get them to trust you