Willi around 100 students scheduled to be in that 9 am Monday morning lecture, it is no surprise that almost 20 people actually make it to the class and only 10 of them arc still awake after the first IS minutes; it is not even a surprise that most of them are still in their pyjamas (睡衣). Obviously, students are terrible at adjusting their sleep cycles to their daily schedule.
All human beings possess a body clock. Along with other alerting (警报) systems, this governs the sleep/wake cycle and is therefore one of the main processes which govern sleep behaviour. Typically, the preferred sleep/wake cycle is delayed in adolescents, which leads to many students not feeling sleepy until much later in the evenings. This typical sleep pattern is usually referred to as the "night owl" schedule of sleep.
This is opposed to the "early bird" schedule, and is a kind of disorder where the individual tends to stay up much past midnight. Such a person has great difficulty in waking up in the mornings. Research suggests that night owls feel most alert and function best in the evenings and at night. Research findings have shown that about 20 percent of people can be classified as "night owls" and only 10 percent can be classified as "early birds" - the other 70 percent are in the middle. Although this is clearly not true for all students, for the ones who are true night owls this gives them an excellent excuse for missing their lectures which unfortunately fall before midday.
What docs the author stress in Paragraph I?

A．Many students are absent from class.

B．Students are very tired on Monday mornings.

C．Students do not adjust their sleep patterns well.

D．Students are not well prepared for class on Mondays.

Which of the following is true according to Paragraph 2?

A．Most students prefer to get up late in the morning.

B．Students don't sleep well because of alerting systems.

C．One's body clock governs the sleep/wake cycle independently.

D．Adolescents' delayed sleep/wake cycle isn't the preferred pattern.

Which of the following is closest in meaning to the underlined word "classified"?

A．Criticised.

B．Grouped.

C．Organised.

D．Named.

What docs the text mainly talk about?

A．Functions of the body clock.

B．The "night owl" phenomenon.

C．Human beings' sleep behaviour.

D．The school schedule of "early birds".