单选题已知E(X)=1，E(X)2=3，用切比雪夫不等式估计则a的最大值为()

单选题从正方体的6个面中选取3个面，其中有2个面不相邻的选法共有( )种．

单选题设则f(x)的定义域是______．

单选题某公司员工义务献血，在体检合格的人中，O型血的有10人，A型血的有5人，B型血的有8人，AB型血的有3人．若从四种血型的人中各选1人去献血，则不同的选法种数共有( )。

单选题If there is one thing scientists have to hear, it is that the game is over. Raised on the belief of an endless voyage of discovery, they recoil from the suggestion that most of the best things have already been located. If they have, today's scientists can hope to contribute no more than a few grace notes to the symphony of science. A book to be published in Britain this week, The End of Science, argues persuasively that this is the case. Its author, John Horgan, is a senior writer for Scientific American magazine, who has interviewed many of today's leading scientists and science philosophers. The shock of realizing that science might be over came to him, he says, when he was talking to Oxford mathematician and physicist Sir Roger Penrose. The End of Science provoked a wave of denunciation in the United States last year. "The reaction has been one of complete shock and disbelief, "Mr. Horgan says. The real question is whether any remaining unsolved problems, of which there are plenty, lend themselves to universal solutions. If they do not, then the focus of scientific discovery is already narrowing. Since the triumphs of the 1960s—the genetic code, plate tectonics, and the microwave background radiation that went a long way towards proving the Big Bang—genuine scientific revolutions have been scarce. More scientists are now alive, spending more money on research, that ever. Yet most of the great discoveries of the 19th and 20th centuries were made before the appearance of state sponsorship, when the scientific enterprise was a fraction of its present size. Were the scientists who made these discoveries brighter than today's? That seems unlikely. A far more reasonable explanation is that fundamental science has already entered a period of diminished returns. "Look, don't get me wrong," says Mr Horgan. "There are lots of important things still to study, and applied science and engineering can go on for ever. I hope we get a cure for cancer, and for mental disease, though there are few real signs of progress./

单选题函数(x＞1)的最小值为()．

单选题设随机变量X～F(m，n)，令P{X＞Fα(m，n)}=α(0＜α＜1)，若P(X＜k)=α，则k等于______．A．Fα(m，n)B．F1-α(m，n)C．D．

单选题下列命题正确的是( )A．无穷小量的倒数是无穷大量B．无穷小量是绝对值很小很小的数C．无穷小量是以零为极限的变量D．无界变量一定是无穷大量

单选题某人手中握有一把玉米粒，若3粒一组取出，余1粒；若5粒一组取出，也余1粒；若6粒一组取出，也余1粒，则这把玉米粒最少有______粒．

单选题曲线y=xlnx在点（e，e）处法线的斜率为

单选题下列不等式中成立的是{{U}} {{/U}}。 A.sin1＜sin4 B.cos1＜cos4 C.tan1＜tan4 D.cot1＜cot4

单选题已知集合A={2，4，8}，B={2，4，6，8}，则A∪B=（　）

单选题函数在区间[0，4]上的最大值为______A．0B．1C．6D．

单选题设随机变量X1，X2都服从区间[0，4]上的均匀分布，且P{X1≤3，X2≤3}=1，则P{X1＞3，X2＞3}=______A．0B．C．D．

单选题若等差数列{an}满足5a7-a3-12=0，则

单选题某足球邀请赛共有6支球队参加．现将6支球队分成两组，每组3队进行单循环赛，每组前两名进入第二阶段，进行淘汰赛决出冠亚军．本次邀请赛的比赛场次共有( )场．

单选题设，当x≠0时，F(x)=f(x)，若F(x)在点x=0处连续，则F(0)等于______

单选题马克思指出：“如果物没有用，那么其中包含的劳动也就没有用，不能算作劳动，因此不形成价值。”这段话说明______。 A．价值的存在以物的有用性为前提 B．价值的存在与物的有用性互为前提 C．只要物是有用的，它就有价值 D．物越是有用就越有价值

单选题设f(x)为连续的奇函数，则等于____．A．2af(x)B．C．0D．f(a)-f(-a)

单选题箱子中有2个红球，3个白球，从中任取2球，则取到的球是一红一白的概率是______。