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　　Part Ⅱ Reading Comprehension(Skimming and Scanning)(15 minutes)

　　Directions：In this part，you will have 15 minutes to go over the passage quickly and answer the questions an Answer Sheet 1. For question 1—7 choose the best answer from the four choices marked /A)，B)，C)and D). For questions 8—10 complete the sentences with the information given in the passage.

　　Supersize Surprise

　　Ask anyone why there is an obesity epidemic and they will tell you that it’s al down to eating too much and burning too few calories. That explanation appeals to common sense and has dominated efforts to get to the root of the obesity epidemic and reverse it/ yet obesity researchers are increasingly dissatisfied with it. Many now believe that something else must have changed in our environment to precipitate(促成) such dramatic rises in obesity over the past 40 years or so. Nobody is saying that the “big two” – reduced physical activity and increased availability of food – are not important contributors to the epidemic, but they cannot explain it all.

　　Earlier this year a review paper by 20 obesity experts set out the 7 most plausible alternative explanations for the epidemic. Here they are.

　　1. Not enough sleep

　　It is widely believed that sleep is for the brain, not the body. Could a shortage of shut-eye also be helping to make us fat?

　　Several large-scale studies suggest there may be a link. People who sleep less than 7 hours a night tend to have a higher body mass index than people who sleep more, according to data gathered by the US National Health and Nutrition Examination Survey. Similarly, the US Nurses’ Health Study, which tracked 68,000 women for 16 years, found that those who slept an average of 5 hours a night gained more weight during the study period than women who slept 6 hours, who in turn gained more than whose who slept 7.

　　It’s well known that obesity impairs sleep, so perhaps people get fat first and sleep less afterwards. But the nurses’ study suggests that it can work in the other direction too: sleep loss may precipitate weight gain.

　　Although getting figures is difficult, it appears that we really are sleeping less. In 1960 people in the US slept an average of 8.5 hours per night. A 2002 poll by the National Sleep Foundation suggests that the average has fallen to under 7 hours, and the decline is mirrored by the increase in obesity.

　　2. Climate control

　　We humans, like all warm-blooded animals, can keep our core body temperatures pretty much constant regardless of what’s going on in the world around us. We do this by altering our metabolic(新陳代新的) rate, shivering or sweating. Keeping warm and staying cool take energy unless we are in the “thermo-neutral zone”, which is increasingly where we choose to live and work.

　　There is no denying that ambient temperatures(環境溫度) have changed in the past few decades. Between 1970 and 2000, the average British home warmed from a chilly 13C to 18C. In the US, the changes have been at the other end of the thermometer as the proportion of homes with air conditionings rose from 23% to 47% between 1978 and 1997. In the southern states – where obesity rates tend to be highest – the number of houses with air conditioning has shot up to 71% from 37% in 1978.

　　Could air conditioning in summer and heating in winter really make a difference to our weight? Sadly，there is some evidence that it does at least with regard to heating. Studies show that in comfortable temperatures we use less energy.