【单选题】

Because they absorb heat from the environment rather than generate much of their own, reptiles are said to be ectotherms, a term identifying their major source of body heat as being external.Ectotherms heat directly with solar energy by basking in the sun, rather than through the metabolic breakdown of food, as in mammals and birds. This means that a reptile can survive on less than 10 percent of the calories required by a mammal of equivalent size.

2. Which sentence below best expresses the essential information in the highlighted sentence in the passage
A．Because a reptile heats with solar energy, it requires less than 10 percent of the calories that a mammal of the same size needs.
B．A、reptile obtains only 10 percent of its calories from the metabolic breakdown of food; it obtains the rest by basking in the sun.
C．Some reptiles and mammals are equal in size, but they require vastly different quantities of calories for survival.
D．Reptiles need to spend only 10 percent of their time eating because they do not need as many calories as mammals of equal siz