单选题When Dr. John W.Gofman, professor of medical physics at the University of California and a leading nuclear critic, speaks of "ecocide" in his adversary view of nuclear technology, he means the following: A large nuclear plant like that in Kalkar, the Netherlands, would produce about 200 pounds of plutonium each year. One pound, released into the atmosphere, could cause 9 billion cases of lung cancer. This waste product must be stored for 500,000 years before it is of no further danger to man. In the anticipated reactor economy, it is estimated that there will be 10,000 tons of this material in Western Europe, of which one table-spoonful of plutonium-239 represents the official maximum permissible body burden for 200,000 people. Rather than being biodegradable, plutonium destroys biological properties. In 1972 the U.S. Occupational Safety and Health Administration ruled that the asbestos level in the work place should be lowered to 2 fibers per cubic centimeter of air, but the effective date of the ruling has been delayed until now. The International Federation of Chemical and General Workers' Unions report that the 2-fiber standard was based primarily on one study of 290 men at a British asbestos factory. But when the workers at the British factory had been reexamined by another physician, 40--70 percent had X-ray evidence of lung abnormalities. According to present medical information at the factory in question, out of a total of 29 deaths thus far, seven were caused by lung cancer. An average European or American worker comes into contact with six million fibers a day. "We are now, in fact, finding cancer deaths within the family of the asbestos worker," states Dr. Irving Selikoff, of the Mount Sinai Medical School in New York. It is now also clear that vinyl chloride, a gas from which the most widely used plastics are made, causes a fatal cancer of the blood-vessel cells of the liver. However, the history of the research on vinyl chloride is, in some ways, more disturbing than the "Watergate cover-up." "There has been evidence of potentially serious disease among polyvinyl chloride workers for 25 years that has been incompletely appreciated and inadequately approached by medical scientists and by regulatory authorities," summed up Dr. Selikoff in the New Scientist. At least 17 workers have been killed by vinyl chloride because research over the past 25 years was not followed up. And for over 10 years, workers have been exposed to concentrations of vinyl chloride 10 times the "safe limit" imposed by Dow Chemical Company. (422 words)Notes: plutonium 钚。asbestos 石棉。polyvinyl chloride 聚氯乙烯。

单选题双纽线(x2+y2)2=x2-y2所围成的区域面积可用定积分表示为______A．B．C．D．

单选题设函数f(u，v)连续，，则A．f(x，y)．B．f(y，x)．C．D．

单选题△ABC中，AB=5，AC=3，∠A=x，该三角形BC边上的中线长是x的函数y=f(x)，则当x在(0，π)中变化时，函数f(x)取值的范围是( )．

单选题设函数在x=0处连续，则a等于______．A．2B．C．1D．-2

单选题一个大干1的自然数的算数平方根为a，则与这个自然数左右相邻的两个自然数的算数平方根分别为()。

单选题已知关于x的一元二次方程8x2+(m+1)x+m-7=0有两个负数根，那么实数m的取值范围是( )。 A．m＞7 B．m＜7 C．m＞1 D．m＜1

单选题下列等式或结论正确的是

单选题若，则直线y=kx+(m+n)一定经过第______象限．

单选题正方形ABCD边长为1，延长AB到E，延长BC到F，使得BE=CF=1，DE分别和BC，AF交于H，G，如图6-64．则四边形ABHG的面积为()．

单选题已知4阶方阵A=[α1，α2，α3，α4]，α1，α2，α3，α4均为四维列向量，其中α1，α2线性无关，若α1+2α2-α3=β，α1+α2+α3+α4=β，2α1+3α2+α3+2α4=β，k1，k2为任意常数，那么Ax=β的通解为A．B．C．D．

单选题已知∠A为锐角，且，那么()．

单选题设，则下列命题中不正确的是A．B．C．D．

单选题x=0为函数（）

单选题甲、乙两商店某种商品的进货价格都是200元，甲店以高于进货价格20%的价格出售，乙店以高于进货价格15%的价格出售，结果乙店的售出件数是甲店的2倍。扣除营业税后乙店的利润比甲店多5400元。若设营业税率是营业额的5%，那么甲、乙两店售出该商品各为______件。

单选题设非齐次线性微分方程y'+P(x)y=Q(x)有两个不同的解y1(x)，y2(x)，C为任意常数，则该方程的通解是______．

单选题设是三阶可逆矩阵，B是三阶矩阵，且则B相似于______A．B．C．D．

单选题S n 为{a n }前n项和，a 1 =3，S n +S n+1 =3a n+1

单选题图5-1所示的f(x)在区间(a，b)上连续，则由曲线y=f(x)，直线x=a，x=b及x轴所围成的平面图形的面积S等于()．

单选题一出租车司机从饭店到火车站途中有6个交通岗，假设他在各交通岗遇到红灯这一事件是相互独立的，并且概率都是．那么这位司机遇到红灯前，已经通过了2个交通岗的概率是()．