In this section, you will hear several passages.
Listen to the passages carefully and then answer the questions that
follow. Questions 11 to 14 are based on the
following passage. At the end of the passage, you will be giv en 20 seconds to
answer the questions. Now, listen to the
passage. How long will be the optimal span of the nap
A．About three quarters. B．No more than an hour. C．Less than half an hour. D．Fifteen minutes.