Questions 15 to 17 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
Now, listen to the passage. Which of the following is the main idea of the passage

A．Evolution has equipped all creatures with a regular pattern of sleeping and waking.
B．The study of sleep is an important part of the evolutionary theory.
C．Sleeping patterns must be taken into consideration in the designing of robots.
D．The sleeping pattern of a living creature is determined by the food it eats.