Which statement is true regarding thermoregulation?

• A. An ectotherm such as a lizard does not maintain a fairly constant body temperature.
• B. Endotherms must always maintain a fairly constant body temperature to survive.
• C. In furry animals, raised hairs keep the animal cooler than lowered hairs.
• D. A dilated blood vessel conserves more heat than a constricted one.
• E. Ectotherms generally do not conserve body heat as effectively as do marine mammals.