题目

（2013衡水中学调研）如图所示，倾角为30°的光滑杆上套有一个小球和两根轻质弹簧，两弹簧的一端各与小球相连，另一端分别用销钉Ｍ、Ｎ固定于杆上，小球处于静止状态．设拔去销钉Ｍ（撤去弹簧ａ）瞬间，小球的加速度大小为6ｍ/s2．若不拔去销钉Ｍ，而拔去销钉Ｎ（撤去弹簧ｂ）瞬间，小球的加速度可能是（ｇ取10ｍ/s2）：           （    ） A．11ｍ/ s2，沿杆向上 B．11ｍ/ s2，沿杆向下 C．1ｍ/ s2，沿杆向下 D．1ｍ/ s2，沿杆向上Using too much water or throwing rubbish into our rivers are clear ways that humans canPut our water supply in danger ,but we also affect our water supply in less obvious ways .You may wonder how paving(铺砌) a road can lead to less useable fresh water . A majorPart of the water we use every day is groundwater . Groundwater does not come from lakes or rivers .It come from underground . The more roads and parking lots we pave ,the less water canFlow into the ground to become groundwater . Human activity is not responsible for all water shortages(短缺). Driver climates are of course more likely to have droughts(干旱) than areas with more rainfall ,but in any case, good management can help to make sure there is enough water to meet our basic needs . Thinking about the way we use water every day can make a big difference ,too In the United States ,a family of four can use 1.5tons of water a day ! This shows how much we depend on water to live ,but there’s a lot we can do to lower the number .You can take steps to save water in your home .To start with ,use the same glass for your drinking water all day .Wash it only once a day .Run your dishwasher (洗碗机)only when it is full 。Help your parents fix any leaks in your home . You can even help to keep our water supply clean by recycling batteries instead of throwing them away .1.Which of the following is most likely to lead to less groundwater ?A. Using river water B .Throwing batteries away .C. paving parking lots D. Throwing rubbish into lakes .2.What can be inferred from the text ?A. All water shortages are due to human behavior .B. It takes a lot of effort to meet our water needs .C. There is much we can do to reduce family size .D. The average family in America makes proper use of water .3.The last paragraph is intended to .A. show us how to fix leaks at home B. tell us how to run a dishwasher C. prove what drinking glass is best for us D. suggest what we do to save water at home 4.The text is mainly about .A. Why paving roads reduces our water B. how much we depend on water to live C. why droughts occur more in dry climatesD. how human activity affects our water supply