Passage 2Do you sleep between seven to nine hours per night? According to the experts, this is the amount needed, on average, to keep our minds alert and our bodies healthy — but many people aren't getting enough.In the United States, for example, half the population sleeps less than seven hours during the week, according to the 2013 International Bedroom Poll. To make up, many of them resort to catching up when circumstances allow — whether it's sleeping in at the weekend or napping during the day. But this catch-up can have its own impact on your body and when this catch-up becomes too much, it could even be a sign of a hidden health problem.The much-loved weekend snooze (小睡) stems from the need to catch up on sleep lost during the week. "That's an attempt to pay back sleep deprivation," says Charles Czeisler, chief of the Division of Sleep and Circadian Disorders at the Brigham and Women's Hospital, in Boston. But Czeisler is not an advocate of sleeping late at the weekend. He calls it "sleep binging (放纵)" and says it's a break from consistency that leads to further disruption of our sleep cycles.The extra hours of sleep, but more importantly the later time of awakening, at the weekend, lead to confusion in the body when people return to their weekday routine — something Czeisler defines as "social jet lag.""If you're getting up at 6 am and then noon, that's the equivalent of Boston to Paris in time zones," he says. Making a habit of this is not a healthy lifestyle to lead, according to Czeisler. "This has adverse health consequences ... it's better to have consistency of sleep," he says.It's worth paying attention to the hours you spend sleeping, and in bed, as a means of monitoring and maintaining your health and well-being. "Duration, timing and quality of sleep are the key factors," says Czeisler.More studies are needed to truly understand the causes of the links seen between excessive sleep and various health conditions, but for the time being it may be wise to avoid those weekend binges and instead inject some routine into your dreams.(1) (单选题)According to the experts, how many sleeping hours are considered to be unhealthy per night?A.Six hours.B.Seven hours.C.Eight hours.D.Nine hours.(2) (单选题)Why do many Americans love to sleep late at the weekend?A.Because they want to live a healthy life.B.ecause they want to keep consistency of sleep.C.Because they want to better prepare for the work in the following week.D.Because they want to make up for the sleeping time lost in previous days.(3) (单选题)What does Czeisler mean by saying "social jet lag" in Para. 4?A.Confusion resulting from a long-distance airplane travel.B.Tiredness resulting from the lack of sleep in the weekday.C.Discomfort resulting from changes of sleeping patterns.D.Social stress related to the weekday routine.(4) (单选题)According to the passage, what might be considered as a healthy sleeping habit?A.Sleep late at the weekend.B.Having a nap at noon.C.Sleeping more than eight hours per night.D.Having a regular sleep pattern.(5) (单选题)What do we learn about sleep fron this passage?A.The sleep quality is more important than the time.B.The more we sleep, the healthier we will be.C.A frequent desire to sleep late could be a sign of a health problem.D.Most people have satisfactory sleep during the weekday and the weekend.A. ①③B. ①④C. ②③D. ②④