题目

如图所示，将三个物体放入水中，A 漂浮在水面上(部分露在水面以上)，B 悬浮在水中，C 沉至容器底(对容器底有压力)。已知 A、B 质量相等，B、C 体积相等。则下列说法正确的是（） A . C 的体积大于 A 的体积 B . A 所受浮力大于 C 所受浮力 C . B 所受浮力大于 C 所受浮力 D . 三物体所受浮力相等 答案：D In China, more and more middle school students are getting shorter sleeping time than before. More students sleep less than nine hours every night, because they have much homework to do. Some homework is given by their teachers, and some by their parents. Also, some students don’t know how to save time. They are not careful enough while they do their homework, so it takes them a lot of time. Some students spend too much time watching TV or playing computer games. They stay up very late. Some students have to get up early every morning on weekdays to get to school on time by bus of by bike . It can be a long way from home to school. It will probably make them sleepy during school hours. Schools and parents should cut down some of the homework so that our children can enjoy more than nine hours of sleep every night for their health. For children, they should make the most best use of their time. When they have enough time for sleeping .They will find it much better for both their study and health. 1 What make most students sleep less than nine hours every night?        A. Doing housework.     B. Playing computer games.        C. Doing homework.     D. Watching TV. 2 Who else gives children some homework to do except their teachers according to the article?        A. Their parents.    B. Other students.   C. Nobody else.     D. They themselves. 3 How many hours of sleep is good for students’ health?        A. Only 9 hours.    B. Over 9 hours.    C. 8 hours.     D. Less than 9 hours. 4 Which is the following is NOT true?        A. Some students are careless that they spent much time on the homework.        B. All the students stay up late for their homework.        C. Schools and parents should take care of children’s health.        D. Children should be given less homework.