单选题设f(x)为区间[a，b]上的连续函数，则曲线y=f(x)与直线x=a，x=b，y=0所围成的封闭图形的面积为()

单选题具有特解y 1 =e -x ，y 2 =2xe -x ，y 3 =3e x 的三阶常系数齐次线性微分方程是

单选题我国对资本主义工商业的社会主义改造所采取的基本政策是______。 A．加工订货 B．统购包销 C．和平赎买 D．公私合营

单选题 下列命题中，不正确的是 A、欧氏空间中保持任两个向量的距离不变的线性变换必为正交变换， B、欧氏空间中把某一标准正交基变为标准正交基的线性变换为正交变换。 C、欧氏空间中保持任两向量的夹角不变的线性变换必为正交变换。 D、欧氏空间中何持内积不变的线性变换必为正交变换。

单选题直线ax-by=0与圆x2+y2-ax+by=0(a,b≠0)的位置关系是( )。

单选题1929年4月，毛泽东主持制定的《兴国土地法》对《井冈山土地法》的一个原则性纠正是______。 A．改土地归工农民主政府所有为归农民自己所有 B．改没收一切土地为没收一切公共土地及地主阶级的土地 C．改按人口平分土地为按劳动力分配土地 D．改“抽多补少”为“抽肥补瘦”

单选题设X1，X2，…，Xn是来自总体N(μ，σ2)(σ＞0)的简单随机样本，记统计量，则ET=______。A.σ2B.μ2C.σ2+μ2D.σ2-μ2

单选题设随机变量X与Y分别服从正态分布N(-1，2)与N(1，2)，且X与Y不相关，aX+Y与X+bY亦不相关，则一定有______

单选题设，则下列结论中错误的是()．

单选题设f(x，y)为连续函数，则使成立的充分条件是()

单选题设u(x，y)在点M0(x0，y0)处取极小值，并且均存在，则

单选题装台机器需要甲，乙，丙三种部件各一件，现库中存有这三种部件共270件，分别用甲，乙，丙库存件数的装配若干机器，那么原来存有甲种部件()．

单选题设，若，则n的最小值为()。A．7B．8C．9D．10

单选题设常数k≠0，则为______

单选题若双曲线经过点，且它的两条渐近线的方程是，则双曲线方程是()。

单选题It is no longer just dirty blue-collar jobs in manufacturing that are being sucked offshore but also white-collar service jobs, which used to be considered safe from foreign competition. Telecoms charges have tumbled, allowing workers in far-flung locations to be connected cheaply to customers in the developed world. This has made it possible to offshore services that were once non-tradable. Morgan Stanley's Mr. Roach has been drawing attention to the fact that the "global labour arbitrage" is moving rapidly to the better kinds of jobs. It is no longer just basic data processing and call centres that are being outsourced to low-wage countries, but also software programming, medical diagnostics, engineering design, law, accounting, finance and business consulting. These can now be delivered electronically from anywhere in the world, exposing skilled white-collar workers to greater competition. The standard retort to such arguments is that outsourcing abroad is too small to matter much. So far fewer than lm American service-sector jobs have been lost to off-shoring. Forrester Research forecasts that by 2015 a total of 3.4m jobs in services will have moved abroad, but that is tiny compared with the 30m jobs destroyed and created in America every year. The trouble is that such studies allow only for the sorts of jobs that are already being off-shored, when in reality the proportion of jobs that can be moved will rise as IT advances and education improves in emerging economies. Alan Blinder, an economist at Princeton University, believes that most economists are underestimating the disruptive effects of off-shoring, and that in future two to three times as many service jobs will be susceptible to off-shoring as in manufacturing. This would imply that at least 30% of all jobs might be at risk. In practice the number of jobs off-shored to China or India is likely to remain fairly modest. Even so, the mere threat that they could be shifted will depress wages. Moreover, says Mr. Blinder, education offers no protection. Highly skilled accountants, radiologists or computer programmers now have to compete with electronically delivered competition from abroad, whereas humble taxi drivers, janitors and crane operators remain safe from off-shoring. This may help to explain why the real median wage of American graduates has fallen by 6% since 9000, a bigger decline than in average wages. In the 1980s and early 1990s, the pay gap between low-paid, low-skilled workers and high-paid, high-skilled Workers widened significantly. But since then, according to a study by David Autor, Lawrence Katz and Melissa Kearney, in America, Britain and Germany workers at the bottom as well as at the top have done better than those in the middle-income group. Office cleaning cannot be done by workers in India. It is the easily standardised skilled jobs in the middle, such as accounting, that are now being squeezed hardest. A study by Bradford Jensen and Lori Kletzer, at the Institute for International Economics in Washington D. C., confirms that workers in tradable services that are exposed to foreign competition tend to be more skilled than workers in non-tradable services and tradable manufacturing industries.

单选题一只船顺流而行的航速为30km/h，已知顺水航行3h和逆水航行5h的航程相等，则此船顺水漂流1h的航程为( )km．

单选题Some would consider that an infringement of good manners whereas others would not. A. an example B. a violation C. a problem D. an indication

单选题设z=x 3 -3x-y，则它在点(1，0)处

单选题设x1，x2是方程x2-(a2+2)x+a=0(1≤a≤3)的两个实根，则的最小值为()．