题目

图为一种简易电热水器的示意图，使用开关S可以使热水器处于加热或保温状态。在热水器的蓄水桶中装水至最高水位时，桶底受到水的压强是_________Pa；闭合开关S时，热水器处于_________状态(选填“加热”或“保温”)。桶中质量为10kg的水由28℃加热到98℃时吸收热量为_________J。[已知c水=4.2×103J／(kg・℃)]  第三部分 阅读理解（共20小题；每小题2分，满分40分）   A Forests have always been useful and important to man who make use of them in many ways. Every day trees are serving man everywhere. Trees supply man with fruits and building materials in the form of wood, without trees it would be impossible to build houses, boats, bridges and so on. Furniture such as desks, chairs and beds is made of wood, trees can stop man from terrible heat. They're also useful in preventing good and rich top soil from being washed away during heavy rains.      If there were no trees, heavy rains would wash away the rich surface soil that is so important to plants. The result is that the land will become a desert. There are plenty of desert areas in the world. A long time ago these desert areas used to be very rich areas, but man in the past had no enough knowledge about science of nature, they cut down too many trees in the area where they lived and never planted new ones. By and by the rich surface soil was blown and washed away by strong winds and heavy rains. In the end the rich land changed into useless deserts where nothing could grow. 56 . According to the passage,__________.     A. a long time ago, man didn't know how to make use of wood     B. trees are not as useful as they were in the past     C. trees were more found in the past than they are today     D. people have always found trees useful 57. "Top soil" means____________and is          .     A. useless soil; of no use for plants     B. soil on the surface of the earth; good for plants     C. soil found under the earth; found under the roots of trees     D. dry soil in the desert areas; bad for plants 58. Some deserts were once__________.     A. very good lands   B. covered by ice   C. very cold       D. dry and useless 59. If there were no trees,______________.    A. the land would become better             B. heavy rains would be very clean    C. the rich soil couldn't be kept              D. there wouldn't any plants 60. From the passage, we know that man must__________.         A. do nothing to keep the balance of nature     B. take his best to keep the balance of nature     C. try his best to keep the balance of nature D. do his  best to stop the balance of nature