题目

《九章算术》中记载，堑堵是底面为直角三角形的直三棱柱，阳马指底面为矩形，一侧棱垂直于底面的四棱锥.在堑堵 中，，当阳马 体积为时，堑堵的外接球的体积的最小值（ ）A. B. C. D. 答案：【答案】B【解析】设AC＝x，BC＝y，由阳马B﹣A1ACC1体积，得到，结合基本不等式求得外接球半径由此能求出外接球体积．设AC＝x，BC＝y，由题意得x＞0，y＞0，又 体积为， 堑堵的外接球即以 为棱的长方体的外接球故 ，当且仅当x＝y时，取等号，∴外接球的体积为 故选B．    Scientists are studying new information about storm activity in the Atlantic Ocean．Weather experts say the North Atlantic had more storms this past year than during most years．The area had a record of five major hurricanes with wind speeds of one- hundred- ninety kilometers an hour or greater.     Researchers also note an increase in the number of areas setting new records for high and low temperatures.     More severe storms have been reported in some areas．Other areas have suffered from a severe lack of rain.     Alex Green of the University of Florida believes a general warming in Earth’s atmosphere is to blame．This warming is commonly called the Green-house Effect.     Scientists believe it is caused by burning fuels such as oil and coal．Many scientists say the pollution released by burning the fuels enters the atmosphere and may lead to higher temperatures on Earth.     Professor Green says the more carbon dioxide released into the atmosphere, the more extreme weather systems we can expect.     But not all researchers agree．Tom Ross is a weather expert with the National Climatic Data Center in North Carolina．Mister Ross says what is happening now could become less of an issue at a future date．He notes that only twenty years ago some scientists were warning about the start of a new ice age.     Mister Ross says more information needs to be collected before scientists can blame current weather conditions on the Greenhouse Effect．However, Mister Green says that by the time scientists agree about the problem it may be too late to do anything about it. 1．The number of areas setting new records for high and low temperature which have suffered from a severe lack of rain or more severe storms is ________; A．one B．two C．under three D．above three 2． The underlined “the Greenhouse Effect” means ________. A．a general warming in Earth’s atmosphere B．that the more carbon dioxide released into the atmosphere, the more extreme weather systems we can expect C．burning fuels such as oil and coal D．that the pollution released by burning the fuels enters the atmosphere 3．What is your opinion after reading the last paragraph? My opinion is that ________. A．all the scientists can blame current weather conditions on the Greenhouse Effect B．not all the scientists agree about the Greenhouse Effect C．it is never too late to do anything almost Greenhouse Effect D．it maybe too late to do anything about Greenhouse Effect 4．The main idea of this passage is ________. A．storms and the environment B．the pollution caused by burning the fuels C．the change of the environment and study D．the Greenhouse Effect