单选题已知|a|=5，|b|=7，ab＜0，则|a-b|=______．

单选题展开式的常数项为{{U}}{{/U}}。A.3511B.3990C.4350D.4351

单选题设B等于()

单选题设为持续函数，则是在点处获得极值(   ) 

单选题已知关于x的方程x 2 +4x+2a|x+2|+6-a=0有两个不等的实根，则系数a的取值范围是______．

单选题若△ABC的三边为a、b、c，且满足a 2 +b 2 +c 2 =ab+ac+bc，则△ABC为______．

单选题不等式x2-2x0的解集为（　）

单选题设f(x)在x0处不连续，则A．f(x0)必存在B．f'(x0)必不存在______C．必存在D．必不存在

单选题已知关于x的方程x2-6x+(a-2)|x-3|+9-2a=0有两个不同的实数根，则系数a的取值范围是( )．

单选题下列命题中正确的是

单选题设则B-1为______.

单选题设A为四阶方阵，且满足A 2 =A，则秩r(A)+秩r(A-E)=

单选题已知f(x)在x0处可导，且有，则f'(x0)等于()A．-4B．-2C．2D．4

单选题已知离散型随机变量X的概率分布为则E(X)=______

单选题的值等于()．A．0B．nC．-nD．2n

单选题The modern university is the ideal environment for the creation and transfer of knowledge that drives national competitiveness in an increasingly global era. Its most effective form is the American adaptation of the European model, in which teaching, leaning and research are integrated into a single institution. Indeed, the American university has proved capable of almost anything, from developing advanced economic theories to creating new life forms. Many national leaders understand that the university is the critical catalyst for America's adaptability, economic robustness and emergence as a great power. And they are moving aggressively to catch up. The universities created by emerging economies beginning in the 1990s and through 2020 will likely play a decisive role in reshaping the global balance of economic power. That is bad news for the United States. The past two decades of American university development have been characterized largely by self-satisfaction arising from steady progress by the top 20 or so research universities. And America as a nation has 1Seen coasting. Since 2000, the United States has lost its edge in the graduation of engineers and technologists. The country no longer dominates scientific discovery, innovation or exploration. Most important, the United States has not launched any effort to build new institutions to accommodate its increasingly diverse population of more than 300 million. The result is that America's university system, despite its historical pre-eminence, has ceased to grow. Furthermore, America's university system has failed to adapt to the dramatic demographic shifts occurring as a result of social mobility and immigration. America needs to realize that its universities face real competition from the rest of the world to attract the best and the brightest, to secure resources and to provide environments that educate and inspire. This is not to say that the best American universities are no longer the leaders in discovery and innovation. It is to say that the success of the higher-education system must be measured by more than just innovations. Its long-term performance depends on its ability to provide learning to a broad cross sections of citizens, to advance national proficiency in math and science and to create an adaptable work force, as well as to develop a national appreciation for discovery, entrepreneurship and the creative process. In China and elsewhere, these are the goals of the new universities being built. In the United States, we need to move from a national self-confidence based on past success to one built on the knowledge that we are advancing a system of higher education that will meet our future needs. This will require that policymakers, business leaders and universities rededicate themselves to creating comprehensive learning and discovery environments; design entirely new models and methods for teaching, and then take action to implement them.

单选题（　）

单选题今年王先生的年龄是他父亲年龄的一半，他父亲的年龄又是他儿子的15倍，两年后他们主人的年龄之和恰好是100岁，那么王先生今年的岁数是( )．

单选题设ξ 1 =(1，-2，3，2) T ，ξ 2 =(2，0，5

单选题已知θ是第三象限的角，且有，则sin2θ=()。A．B．C．D．