单选题某学生要邀请10位同学中的4位参加一项活动，其中有2位同学要么都请，要么都不请，则不同的邀请方法有( )种．

单选题一个坛子里有编号为1，2，…，12的12个大小相同的球，其中1到6号球是红球，其余的是黑球。若从中任取两个球，则取到的都是红球，且至少有1个球的号码是偶数的概率为______。A．B．C．D．E．以上答案均不正确

单选题设随机变量X，Y相互独立，且X～N(0，1)，Y～N(1，1)，则______．A．P(X+Y≤0)=B．P(X+Y≤1)=C．P(X-Y≤0)=D．P(X-Y≤1)=

单选题已知某厂每天生产x千克产品的总成本为(元)，要使产品的平均成本最小，每天应生产该产品()．

单选题The idea that some groups of people may be more intelligent than others is one of those hypotheses that dare not speak its name. But Gregory Cochran is (1) to say it anyway. He is that (2) bird, a scientist who works independently (3) any institution. He helped popularize the idea that some diseases not (4) thought to have a bacterial cause were actually infections, which aroused much controversy when it was first suggested. (5) he, however, might tremble at the (6) of what he is about to do. Together with another two scientists, he is publishing a paper which not only (7) that one group of humanity is more intelligent than the others, but explains the process that has brought this about. The group in (8) are a particular people originated from central Europe. The process is natural selection. This group generally do well in IQ test, (9) 12-15 points above the (10) value of 100, and have contributed (11) to the intellectual and cultural life of the West, as the (12) of their elites, including several world-renowned scientists, (13) . They also suffer more often than most people from a number of nasty genetic diseases, such as breast cancer. These facts, (14) , have previously been thought unrelated. The former has been (15) to social effects, such as a strong tradition of (16) education. The latter was seen as a (an) (17) of genetic isolation. Dr. Cochran suggests that the intelligence and diseases are intimately (18) . His argument is that the unusual history of these people has (19) them to unique evolutionary pressures that have resulted in this (20) state of affairs.

单选题已知某种商品的价格从一月份到三月份的月平均增长速度为10%，那么该商品三月份的价格是其一月份价格的______．

单选题把两个不同的白球和两个不同的红球任意地排成一列，结果为两个白球不相邻的概率是( )．

单选题当x＞0时，曲线______A.有且仅有水平渐近线．B.有且仅有铅直渐近线．C.既有水平渐近线，也有铅直渐近线．D.既无水平渐近线，也无铅直渐近线．

单选题______．A．2B．C．1D．

单选题设A为3阶矩阵，已知I+A，3I-A，I-3A均不可逆，则A一定相似于矩阵()．

单选题已知且f(0)=0，则等于()

单选题 设向量与与都正交，则 A、1 B、2 C、0 D、3

单选题方程的两根分别为等腰三角形的腰a和底b(a＜6)，则该等腰三角形的面积是( )．

单选题如果方程|x|=ax+1有一负根．则a的取值范围是( )．

单选题对三阶矩阵A的伴随矩阵A*先交换第一行与第三行，然后将第二列的一2倍加到第三列得-E，且|A|＞0，则A等于()

单选题在10到100之间插入50个数，使这52个数成等差数列，则插入的整数共有______个．

单选题我国实行的社会主义市场经济是______。 A．有国家宏观调控的市场经济 B．计划和市场各自发挥作用的市场经济 C．完全竞争的市场经济 D．初级市场经济

单选题用50厘米见方的地砖铺地，需要96块，如果改用40厘米见方的地砖，需要( )块．

单选题一件工作，甲、乙合作要2天，人工费2900元，乙、丙合作需4天，人工费2600元，甲、丙合作2天完成了人工费2400元，甲单独做需要的时间和人工费______．