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

单选题设f(x)的定义域是[-1，0]，则的定义域是()。A．B．[-1,0]C．D．

单选题______A．B．π．C．D．

单选题定义在R上的函数f(x)既是偶函数又是周期函数。若f(x)的最小正周期是π，且当x∈[0,]时，f(x)=sinx，则f()的值为()。

单选题设φ(x)是[0，1]上的正值连续函数，a，b为常数，则当区域D={(x，y)|x2+y2≤1}时，A．πa；B．πb；C．π(a+b)；D．

单选题In the United States, the first day-nursery was opened in 1854. Nurseries were established in various areas during the (1) half of the 19th century; most of (2) were charitable. Both in Europe and in the U. S. , the day nursery movement received great (3) during the First World War, when (4) of manpower caused the industrial employment unprecedented numbers of women. In some European countries nurseries were established (5) in munitions plants, under direct government sponsorship. (6) the number of nurseries in the U. S. also rose (7) , this rise was accomplished without government aid of any kind. During the years following the First World War, (8) , Federal, State, and local governments gradually began to exercise a measure of control (9) the day-nurseries, chiefly by (10) them and by inspecting and regulating the conditions within the nurseries. The (11) of the Second World War was quickly followed by an increase in the number of day-nurseries in almost all countries, as women were (12) called upon to replace men in the factories. On this (13) the U.S. government immediately came to the support of the nursery schools, (14) $ 6,000,000 in July, 1942, for a nursery school program for the children of working mothers. Many States and local communities (15) this Federal aid. By the end of the war, in August, 1945, more than 100,000 children were being cared (16) in day-care centers receiving Federal (17) . Soon afterward, the Federal government (18) cut down its expenditures for this purpose and later (19) them, causing a sharp drop in the number of nursery schools in operation. However, the expectation that most employed mothers would leave their (20) at the end of the war was only partly fulfilled.

单选题经过点(1，0)，且切线斜率为3x2的曲线方程是( )