单选题设A，B都是3阶矩阵，将A中第一行的2倍加至第2行得到矩阵A，，将B中第3列乘以得到B1，如果，则AB=

单选题级数(λ为常数)()

单选题设α，β为四维非零列向量，且α⊥β，令A=αβ T ，则A的线性无关特征向量个数为______．

单选题设函数f(x，y)连续，则二次积分等于

单选题设A为n阶矩阵，满足AAT=E，|A|＜0，求|A+E|。

单选题设随机变量X与Y分别服从N(-1，2)和N(1，2)，且X与Y不相关，k1X+Y与X+k2Y也不相关，则______。 A．k1+k2=0 B．k1=k2=0 C．k1+k2≠0 D．k1+k2≠0

单选题Supporters of abortion rights held a lunch recently in honor of a momentous victory for their cause: 40 years ago, New York became the first state to fully legalize abortion. That 1970 law began to reduce the death and injury toll from back-alley abortions and set the stage for the Supreme Court's Roe v. Wade decision in 1973, which made abortion legal nationwide and recognized a constitutional right to privacy. But abortion-rights groups are newly anxious about new assaults on women's reproductive rights, including a fight over abortion that snarled the last days of the health care reform debate. Anti-abortion groups are newly emboldened. Kelli Conlin, head of Naral Pro-Choice New York, told guests at the lunch that "anti-choice forces are mobilizing in every single state to limit a woman's access to abortion in more insidious ways than we can imagine. " As Ms. Conlin was speaking, members of the Oklahoma House were getting ready to override vetoes of two punishing abortion measures. The state's Democratic governor, Brad Henry, rightly viewed these intrusions into women's lives and decision-making as unconstitutional. One of the measures, which seems destined to spawn copycat bills in other states, requires women to undergo an ultrasound before getting an abortion and further mandates that a doctor or technician set up the monitor so the woman can see it and hear a detailed description of the fetus. The other law grants protection from lawsuits to doctors who deliberately withhold fetal testing results that might affect a woman's decision about whether to carry her pregnancy to term. Several states have either passed or are considering bills that would ban abortion coverage in insurance plans sold through the state exchanges established by the federal health care law. A new Utah law criminalizes certain behavior by women that results in miscarriage. Embarking on a road that could lead to the Supreme Court, Nebraska last month banned most abortions at the 20th week of pregnancy based on a questionable theory of fetal pain. About two dozen states are looking at bills to increase counseling requirements or waiting periods prior to abortions. About 20 states are considering new ultrasound requirements. "One in three women in this country will have an abortion in her lifetime, and yet we're having exactly the same discussions and debates we were having forty years ago," Ms. Conlin said. Anti-abortion forces aim ultimately to make abortion illegal. So far, by reducing the number of abortion providers, making insurance coverage more expensive and harder to get, and throwing up other obstacles, they have primarily succeeded in making it harder for women of modest and meager means to obtain a safe and legal medical procedure. The painful decision to end a pregnancy should be made in private between a woman and her doctor—not in politically driven debate among members of Congress and state legislatures.

单选题设总体X～N(0，σ2)(σ2已知)，X1，…，Xn是取自总体X的简单随机样本，S2为样本方差，则下列正确的是______A．B．C．D．

单选题设α 1 ，α 2 ，α 3 是齐次方程组Ax=0的基础解系，那么Ax=0的基础解系还可以是______

单选题将一枚硬币抛n次，X表示正面向上的次数，Y表示反面向上的次数的相反数，则X与Y的相关系数为()

单选题函数在下列哪个区间内有界．(A)(-1，0)．(B)(0，1)．(C)(1，2)．(D)(2，3)．

单选题设区域

单选题设，则能不能相似于对角矩阵的是