单选题已知随机变量X的密度函数则概率P{λ＜X＜λ+a}(a＞0)的值

单选题设f(x)在x=0的某邻域内连续，且(Ⅰ)求f(0)，并证明f'(0)存在并求之．(Ⅱ)设且当x→0时求常数b与k的值．

单选题某公司财务处有甲、乙、丙、丁、戊五名职员，现进行换岗，随机抽取岗位，可与原岗位相同，则有且只有一人与原来的职位一样的概率为______．A．B．C．D．E．

单选题[2010年1月]设a、b为非负实数，则a+b≤。(1)ab≤；(2)a2+b2≤1。

单选题设区域D={(x，y)|x2+y2≤a2，a＞0，y≥0)，则等于______A．B．C．D．

单选题 Old people are always saying that the young are not what they were. The same comment is made from generation to generation and it is always true. It has never been truer than it is today. The young are better educated. They have a lot more money to spend and enjoy more freedom. They grow up more quickly and are not so dependent on their parents. They think more for themselves and do not blindly accept the ideals of their elders. Events which the older generation remembers vividly are nothing more than past history. This is as it should be. Every new generation is different from the one that preceded it. Today the difference is very marked indeed. The old always assume that they know best for the simple reason that they have been around a bit longer. They don't like to feel that their values are being questioned or threatened. And this is precisely what the young are doing. They are questioning the assumptions of their elders and disturbing their complacency. They take leave to doubt that the older generation has created the best of all possible worlds. What they reject more than anything is conformity. office hours, for instance, are nothing more than enforced slavery. Wouldn't people work best if they were given complete freedom and responsibility? And what about clothing? Who said that all the men in the world should wear drab gray suits and convict haircuts? If we turn our minds to more serious matters, who said that human differences can best be solved through conventional politics or by violent means? Why have the older generation so often used violence to solve their problems? Why are they so unhappy and guilt-ridden in their personal lives, so obsessed with mean ambitions and the desire to amass more and more material possessions? Can: anything be right with the rat-race? Haven't the old lost touch with all that is important in life? These are not questions the older generation can shrug off lightly. Their record over the past forty years or so hash't been exactly spotless. Traditionally, the young have turned to their elders for guidance. Today, the situation might he reversed, The old--if they are prepared to admit it--could earn a thing or two from their children. one of the biggest lessons they could learn is that enjoyment is not "sinful". Enjoyment is a principle one could apply to all aspects of life. It is surely not wrong to enjoy your work and enjoy your leisure; to shed restricting inhibitions, It is surely not wrong to live in the present rather than in the past or future. This emphasis on the present is only to be expected because the young have grown up under the shadow of the bomb: the continual threat of complete annihilation. This is their glorious heritage. Can we be surprised that they should so often question the sanity of the generation that bequeathed it?

单选题设，则a与Oz轴的夹角为______A．B．C．D．

单选题设f′(x0)=0，f″(x0)＜0，则必定存在一个正数δ，使得 A．曲线y=f(x)在(x0-δ，x0+δ)是凹的. B．曲线y=f(x)在(x0-δ，x0+δ)是凸的. C．曲线y=f(x)在(x0-δ，x0]单调减少，而在[x0，x0+δ)单调增加. D．曲线y=f(x)在(x0-δ，x0]单调增加，而在[x0，x0+δ)单调减少.

单选题已知向量组α1，α2，α3，α4线性无关，则下列向量组中线性无关的是 (A)α1+α2，α2+α3，α3+α4，α4+α1. (B)α1-α2，α2-α3，α3-α4，α4-α1. (C)α1+α2，α2+α3，α3+α4，α4-α1. (D)α1+α2，α2+α3，α3-α4，α4-α1. [ ]

单选题已知x=1是函数y=x3+ax2的驻点，则常数a=______．A．0B．1C．D．

单选题将4名教师分配到3所中学任教，每所中学至少分配1名教师，则不同的分配方案共有______种 A.12 B.24 C.36 D.48 E.78