题目

关于运动合成，下列说法中正确的是：A．合速度的大小一定比每个分速度的大小都大B．合运动的时间等于两个分运动经历的时间C．两个匀速直线运动的合运动一定也是匀速直线运动D．只要两个分运动是直线运动，合运动一定也是直线运动 答案：BCWorld Sleep Day, on 21st March, was created to bring attention to the growing number of sleep problems. Sleep is a natural part of human life, but many people in the modern world don’t realize it’s very important. As a result, sleep problems are quite common.In 2011, scientists at the University of Athens in Greece did a survey of over 35,000 people in 10 countries around the world, including China, Belgium and South Africa. Among the people, 24 percent said that they did not sleep well, 31.6 percent were diagnosed(诊断) with insomnia(失眠). In addition, 30.7 percent of them have visited doctors for help with sleep problems and 11.6 percent said that they felt very sleepy during the day.The survey found that many people suffer the effects of poor quality sleep, some examples can’t fall asleep and often wake up in the middle of the night. The main reasons of the problems are pressure(压力) from school or work and a fast pace(节奏) of life, but noise pollution and light pollution also affect sleep and cause poor quality sleep. The survey also found that large numbers of people find it hard to sleep at night. The short term effects of this are tiredness and trouble concentrating(专心). If this happens for a long time, the risk of gaining weight and having a heart attack may increase.There are many things you can do to improve the quality of your sleep. First, you should have regular sleep habits. Try to go to bed and wake up around the same time each day. You also need to make your bedroom a cool, dark, quiet place to sleep so that heat, light and noise do not disturb you. At night, you should also avoid things that contain caffeine, such as chocolate, coffee, tea and many soft drinks, as caffeine may keep you from sleeping.Getting a good night's sleep is important for everyone. By following the advice above, you can rest better at night and work better during the day.Have a good sleepWorld Sleep DayWorld Sleep Day was created to make people understand the__1._of sleep.A survey by scientistsOf 35 000 people in 10 countries in the world, 24 percent of the people didn’t have a_2.__sleep.31.6 percent were diagnosed with insomnia.30.7 percent have __3.__ to a doctor for sleep problems.11.6 percent of the people feel __4.__ during the day .__5.__of sleep problemsPeople feel the pressure from school or work .A fast pace of life_6.__to sleep problems as well.Noise and light pollution also cause poor quality sleep.__7.__of sleep problemsSome people aren’t able to fall asleep and often wake up at night.Feeling___8._, people find it hard to concentrate.It’s highly possible that sleepless people easily gain weight and have a heart attack.Ways to__9.__sleep qualityHave regular sleep habits.Make your bedroom cool, dark and quietDon’t drink anything__10.__ caffeine at bedtime.