单选题设随机变量X和Y相互独立且都服从标准正态分布N(0，1)，则______A．B．C．D．

单选题设a是常数，则级数A.当a＞0时收敛．B.当a＞0时发散．C.当a≤1时发散．D.当a≥1时发散．

单选题当x→1时，函数的极限______。

单选题设向量组(Ⅰ)α 1 ，α 2 ，…，α s ，其秩为r 1 ，向量组(Ⅱ)β 1 ，β 2 ，…，β s ，其秩为r 2 ，且β i (i=1，2，…，s)均可由(Ⅰ)α 1 ，α 2 ，…，α s 线性表出，则______

单选题设ξ 1 =(1，-2，3，2) T ，ξ 2 =(2，0，5

单选题设f(x)是以l为周期的周期函数，则之值______

单选题设随机变量X和Y独立同分布，记U=X-Y，V=X+Y，则随机变量U与V必然______． A.不独立 B.独立 C.相关系数不为零 D.相关系数为零

单选题Here in the U. S. a project of moving the government a few hundred miles to the southwest proceeds apace, under the supervision of Senator Robert Byrd of West Virginia. Apart from the usual highways and parks, Byrd has taken a special interest in transplanting pieces of federal agencies from metropolitan Washington to his home state. Strangely, Byrd's little experiment in de-Washingtonization has become the focus of outrage among the very people who are otherwise most critical of Washington and its ways. To these critics, it is the very symbol of congressional arrogance of power, isolation from reality, contempt for the voters, and so on, and demonstrates the need for term limits if not lynching. Consider the good-government advantages of (let's call it) the Byrd Migration. What better way to symbolize an end to the old ways and commitment to reform than physically moving the government? What better way to break up old bureaucracies than to uproot and transplant them, files and all? Second, spreading the government around a bit ought to reduce that self-feeding and self regarding Beltway culture that Washington-phobes claim to dislike so much. Of course there is a good deal of hypocrisy in this anti-Washington chatter. Much of it comes from politicians and journalists who have spent most of their adult lives in Washington and wouldn't care to live anywhere else. They are not rushing to West Virginia themselves, except for the occasional quaint rustic weekend. But they can take comfort that public servants at the Bureau of the Public Debt, at least, have escaped the perils of inside-the-Beltway insularity. Third, is Senator Byrd's raw spread-the-wealth philosophy' completely illegitimate? The Federal Government and government-related private enterprises have made metropolitan Washington one of the richest areas of the country. By contrast, West Virginia is the second poorest state, after Mississippi. The entire country's taxes support the government. Why shouldn't more of the country get a piece of it? As private businesses are discovering, the electronic revolution is making it less and less necessary for work to be centralized at headquarters. There's no reason the government shouldn't take more advantage of this trend as well. It is hardly enough, though, to expel a few thousand midlevel bureaucrats from the alleged Eden inside the Washington Beltway. Really purging the Washington Culture enough to satisfy its noisiest critics will require a mass exodus on the order of what the Khmer Rouge instituted when they took over Phnom Penh in 1975. Until the very members of the TIME Washington bureau itself are traipsing south along 1-95, their word processors strapped to their backs, the nation cannot rest easy. But America's would-be Khmer Rouge should give Senator Byrd more credit for showing the way.

单选题设则在点O(0，0)处，______

单选题设连续型随机变量X的概率密度函数f(x)是一个偶函数，F(x)为X的分布函数，则对任意实数x∈R，有F(-x)+F(x)等于

单选题设常数a＞0，正项级数收敛，则()