The sea horse is an unusual type of fish. Instead of scales, its long, slim body has skin covering bony plates. The head of a sea horse looks very much like a horse's head, with a long snout and pointed ears. A sea horse also has a tail. The tail curls at the end and is used to cling onto coral and seagrasses.

Sea horses are found in warm, tropical waters. They hide from their predators in reefs and seagrass beds. Unlike other fish, sea horses swim upright. Because they cannot swim quickly, they seldom move around much.

Which detail best supports the main idea that sea horses seldom move around much?

A. "A sea horse also has a tail."
B. "Sea horses are found in warm, tropical waters."
C. "Unlike other fish, sea horses swim upright."
D. "Because they cannot swim quickly, they seldom move around much."