One of the signs that sleep is necessary is that all living creatures
a. are harmed by lack of sleep
b. can put off sleep for a time
c. avoid sleep as much as possible
d. can sleep longer than necessary select the best answer from the choices provided a b c d

One of the signs that sleep is necessary is that all living creatures are harmed by lack of sleep. Correct A Sleep serves important evolutionary functions for all animals, because sleep helps animals consolidate memories and learn. Animals sleep according to how much they eat – animals that eat food with a lower caloric density sleep less than others. However, lack of sleep and if the deprivation is long enough it can kill animals.