The Comparative Investigation of Sleep Has Led to an Important

The comparative investigation of sleep has led to an important conclusion: It has suggested that

A) sleep serves an important physiological function.
B) the function of sleep is not some special higher-order cognitive function.
C) sleep may be essential for survival, but it is not necessarily required in large quantities.
D) the amount of time that a members of a particular species tend to sleep is related to how long it takes them to consume enough energy and how susceptible they are to predation when they are sleeping.
E) all of the above