The Descriptive Term Ectotherm, When Applied to Reptiles, Refers to the Fact

The descriptive term ectotherm, when applied to reptiles, refers to the fact that ____.

A) they are warm-blooded
B) their internal body temperature varies with that of the external environment
C) their central body core works best when its temperature is the same as the ambient temperature
D) their optimum temperature for muscle contraction occurs only when the sun provides direct solar heat
E) they maintain their temperature by adjusting the production of metabolic heat