单选题等差数列an中，a1=1，d≠0，并且a3，a4，a6是等比数列，则这个等比数列的第四项是( )．

单选题已知行列式，则k=_______

单选题[2009年10月]命中来犯敌机的概率是99％。 (1)每枚导弹命中率为0．6： (2)至多同时向来犯敌机发射4枚导弹。

单选题48支足球队，等分为8组进行初赛，每组中的各队之间都要比赛一场，初赛中比赛的总场数是{{U}} {{/U}}． A. 288 B. 240 C. 120 D. 48

单选题函数的最大值是()．

单选题设企业生产经营时的总利润、收入和成本均是关于产量的可导函数，若生产某产品产量为x单位，收入和成本分别对产量的变化率(也称边际收入和边际成本)为20-2x和120-10x，且当产量为0时的总收入为0元，固定成本为100元，则生产x单位的总利润是______。 A．4x2-100x-100 B．4x2-100x C．8x-100 D．100x-100

单选题[2009年10月]等差数列{an}的前18项和S18=。

单选题在达成铁路复线工程中，某路段需要铺轨，先由甲工程队独做2天后，再由乙工程队独做3天刚好完成这项任务。已知乙工程队单独完成这项任务比甲工程队单独完成这项任务多用2天，则乙工程队单独完成这项任务各需要______天 A.3 B.4 C.5 D.6 E.7

单选题下列命题①若函数f(x)为[-π，π]上的奇(偶)函数，则f(x)的傅里叶级数必为正(余)弦级数②若函数f(x)在[0，π]上有定义，则f(x)的傅里叶级数展开式是唯一的③设，不论收敛与否，总有④将函数f(x)=x2(0≤x≤1)做偶延拓，得到令x=2得中正确的是

单选题已知f"(0)=a，g"(x)=b，且f(0)=g(0)，则______

单选题 Passage 3 It was (and is) common to think that other animals are ruled by "instinct" whereas humans lost their instincts and ruled by "reason," and that this is why we are so much more flexibly intelligent than other animals. William James, in his book Principles of Psychology, took the opposite view. He argued that human behavior is more flexibly intelligent than that of other animals because we have more instincts than they do, not fewer. We tend to be Mind to the existence of these instincts, however, precisely because they work so well--because they process information so effortlessly and automatically. They structure our thought so powerfully, he argued, that it can be difficult to imagine how things could be otherwise. As a result, we take "normal" behavior for granted. We do not realize that "normal" behavior needs to be explained at all. This "instinct blindness" makes the study of psychology difficult. To get past this problem, James suggested that we try to make the "natural seem strange." It takes a mind debauched by learning to carry the process of making the natural seem strange, so far as to ask for the why of any instinctive human act. In our view, William James was right about evolutionary psychology. Making the natural seem strange is unnatural - it requires the twisted outlook seen, for example, in Gary Larson cartoons Yet it is a central part of the enterprise. Many psychologists avoid the study of natural competences, thinking that there is nothing there to be explained. As a result, social psychologists are disappointed unless they find a phenomenon "that would surprise their grandmothers," and cognitive psychologists spend more time studying how we solve problems we are bad at, like learning math or playing chess, than ones we are good at. But our natural competences - our abilities to see, to speak, to find someone beautiful, to reciprocate a favor, to fear disease, to fall in love, to initiate an attack, to experience moral outrage, to navigate a landscape, and myriad others - are possible only because there is a vast and heterogeneous array of complex computational machinery supporting and regulating these activities. This machinery works so well that we don't even realize that it exists - we all suffer from instinct' blindness. As a result, psychologists have neglected to study some of the most interesting machinery in the human mind.