A streamlined body is a body that is shaped to specifically reduce friction drag when moving.
Flippers and flattened tails are used to propel an animal through the water.
A smooth, almost gutless body is light, which is important when animals have to go through water quickly.
A thick layer of blubber is only used for insulation, and would hamper an animal's progress through water due to its weight.
The answer is B. thick layer of blubber.
