单选题方程x2+y2-z=0表示的二次曲面是( )．

单选题设集合A={x||x-2|≤2，x∈R)，B={y|y=-x2，-1≤x≤2)，则______．

单选题有8个相同的球放到3个不同的盒子里，共有______种不同放法

单选题数例{an2}的前n项和(1)数列{an}是等比数列，公比q=2，首项a1=1(2)数列{an}的前n项和Sn=2n一1

单选题Under pressure from animal welfare groups, two national science teachers associations have adopted guidelines that ban classroom experiments harming animals. The National Association of Biology Teachers and the National Science Teachers Association hope to end animal abuse in elementary and secondary schools and, in turn, discourage students from mishandling animals in home experiments and science fair projects. Animal welfare groups are apparently most concerned with high school students experimenting with animals in extracurricular projects. Barbara Orlans, President of the Scientists' Center for Animal Welfare, said that students have been performing surgery at random, testing known poisonous substances, and running other pathology experiments on animals without even knowing normal physiology. At one science fair, a student cut off the leg and tail of a lizard to demonstrate that only the tail can regenerate, she said. In another case, a student bound sparrows, starved them and observed their behavior. "The amount of abuse has been quite horrifying," Orlans said. Administrators of major science fairs are short-tempered over the teachers' policy change and the impression it has created. "The teachers were sold a bill of goods by Barbara Ortans," said Thurman Grafton, who heads the rules committee for the International Science and Engineering Fair. "Backyard tabletop surgery is just nonsense. The new policies throw cold water on students' inquisitiveness," he said. Grafton said he wouldn't deny that there hasn't been animal abuse among projects at the international fair, but he added that judges reject contestants who have unnecessarily injured animals. The judges have a hard time monitoring local and regional fairs that may or may not choose to comply with the international fair's rules that stress proper care of animals, Grafton said. He said that several years ago, the Westinghouse Science Talent Search banned harmful experiments to animals when sponsors threatened to cancel their support after animal welfare groups lobbied for change. The teachers adopted the new policies also to fend off proposed legislation--in states including Missouri and New York--that would restrict or prohibit experiments on animals. Officials of the two teachers organizations say that they don't know how many animals have been abused in the classroom. On the one hand, many biology teachers are not trained in the proper care of animals, said Wayne Moyer, executive director of the biology teachers' association. On the other, the use of animals in experiments has dropped in recent years because of school budget cuts. The association may set up seminars to teach better animal care to its members. (414 words)Notes: pathology 病理学。lizard 蜥蜴。tabletop 桌面。short-tempered 脾气急躁的。lobby for 游说支持。fend off 躲开。

单选题下列等式不成立的是()

单选题我国著名的地质学家李四光，在对东北的地质结构进行了长期、深入的调查研究后发现，松辽平原的地质结构与中亚细亚极其相似。他推断，既然中亚细亚蕴藏大量的石油，那么松辽平原很可能也蕴藏着大量的石油。后来，大庆油田的开发证明了李四光的推断是正确的。 以下哪项与李四光的推理方式最为相似? A．他山之石，可以攻玉。 B．邻居买彩票中了大奖，小张受此启发，也去买了体育彩票，结果没有中奖。 C．某乡镇领导在考察了荷兰等国的花卉市场后认为要大力发展规模经济，回来后组织全乡镇种大葱，结果导致大葱严重滞销。 D．每到炎热的夏季，许多商店腾出一大块地方卖羊毛衫、长袖衬衣、冬靴等冬令商品，进行反季节销售，结果都很有市场。小王受此启发，决定在冬季种植西瓜。 E．乌兹别克地区盛产长绒棉。新疆塔里木河流域与乌兹别克地区在日照情况、霜期长短、气温高低、降雨量等方面均相似，科研人员受此启发，将长绒棉移植到塔里木河流域，果然获得了成功。

单选题一个棱长为整数n的正方体，表面全涂上红色后，被分成若干个体积都等于1的小正方体．在这些小正方体中，六个面都没有红色的小正方体个数占全部小正方体个数的则n=______．

单选题在x趋向于______时，为无穷小量。

单选题设A为n(n＞1)阶矩阵，已知A的伴随矩阵A*≠0，且α1，α2，α3是非齐次线性方程组Ax=b的不同解，则齐次线性方程组Ax=0的基础解系所含解向量的个数为 (A)0. (B)1. (C)2. (D)3. [ ]

单选题设f(x)在x=1处连续且是周期为2的周期函数，，则曲线y=f(x)过点(-1，f(-1))的切线方程为______。A．y=2(x-1)B．y=2(x+1)C．y=x-1D．y=2x-1