Chinese students aren’t the only ones who have a sleep loss problem. In Australia, teenagers are also missing out on, on average, one hour’s sleep every night during the school week.
Organized activities and homework push bedtimes later, the first large-scale Australian study of children’s sleeping habits has revealed (显示). Their sleep deprivation (剥夺) is enough to cause “serious drop-offs in school performance, attention and memory”, and governments should consider later or flexible school start times, said the study’s leader, Tim Olds.
His survey, of more than 4,000 children aged 9 to 18, found those who slept least did not watch more television but spent their time socializing (相处) with family or friends or listening to music.
“Almost all children get up at 7 or 7:15 — they have to get to school on time,” said Olds. He favors a later start over an earlier finish because he believes organized sports and activities would still consume the latter end of the day.
Olds’ research also establishes lack of sleep as a cause of weight gain in children, and a possible source of future problems with depression, anxiety and increased susceptibility (易感性) to illness.
It was already known that overweight children sleep less, but Professor Olds found sleep duration(时长) was strongly linked to weight across the full range of body sizes. The thinnest children sleep 20 minutes more than the obese. This showed being overweight had no specific effect on sleep patterns, and it was more likely that shorter sleep times stimulate (刺激) appetite and make kids hungry.
The US National Sleep Foundation says teenagers aged 13 to 18 need eight to nine hours’ sleep a night. Younger school-aged kids need 9 to 11 hours.
On that basis, Professor Olds said, half of Australian children are under-sleeping on weekdays and a quarter on weekends.
46. The Australian students surveyed don’t sleep enough because they spend more time on the following EXCEPT _____.
A. organized activities and homework
B. communication with friends and family
C. watching television programs
D. enjoying music 
47.  What effects does lack of sleep directly have on the students according to the survey?
A. They become overweight but begin to eat less than before.
B. They feel more depressed and anxious about their school work.
C. They are more likely to be affected with illness in the future.
D. They pay less attention in class and their memory declines.
48. Which of the following suggestions did Mr. Olds raise?
A. The students should go to bed earlier to have longer sleeping time.
B. The students should participate less in organized activities.
C. The school should put off the start time in the morning.
D. The school should finish earlier in the afternoon.
49. What does "obese" in the sixth paragraph mean?
A. average        B. fat       C. sleepless        D. overeating
50. Which of the following statements is TRUE?
A. Australian students usually take part in activities in the afternoon.
B. More students are short of sleep on weekends than on weekdays.
C. Being overweight has an effect on the length of the sleeping time.
D. The survey suggests that teenagers need 8-9 hours’ sleep a night.