Read the topic sentence.

Dolphins have to use senses other than smelling to help them find their prey.

Which choice represents the “R” in the T-R-I structure for this topic sentence?

They hear mostly through their lower teeth, which are pointed in all different directions to act like radio receivers.
They have excellent vision, which helps them locate their prey even in dim, deep water.
Unlike the shark, which can smell blood from far away, dolphins have no sense of smell at all.
They also have an amazingly keen sense of hearing, much better than people.