单选题设，B为三阶非零矩阵，且AB=0，则

单选题若A，A*和B均是n阶非零矩阵，且AB=0，则必有r(B)=

单选题已知则tan2x=______．A．B．C．D．

单选题若(z-x)2-4(z-y)(y-x)=0，则正确的为( )．

单选题Of all the areas of learning the most important is the development of attitudes.. emotional reactions as well as logical thought processes affect the behavior of most people. "The burnt child fears the fire" is one instance; another is the rise of despots like Hitler. Both these examples also point up the fact that attitudes come from experience. In the one case the experience was direct and impressive; in the other it was indirect and cumulative. The Nazis were influenced largely by the speeches they heard and the books they read. The classroom teacher in the elementary school is in a strategic position to influence attitudes. This is true partly because children acquire attitudes from those adults whose words are highly regarded by them. Another reason it is true is that pupils often devote their time to a subject in school that has only been touched upon at home or has possibly never occurred to them before. To a child who had previously acquired little knowledge of Mexico his teacher's method of handling such a unit would greatly affect his attitude toward Mexicans. The media through which the teacher can develop wholesome attitudes are innumerable. Social studies (with special reference to races, creeds and nationalities), science matters of health and safety, the very atmosphere of the classroom... these are a few of the fertile fields for the inculcation of proper emotional reactions. However, when children go to school with undesirable attitudes, it is unwise for the teacher to attempt to change their feelings by cajoling or scolding them. She can achieve the proper effect by helping them obtain constructive experiences. To illustrate, first-grade pupils afraid of policemen will probably alter their attitudes after a classroom chat with the neighborhood officer in which he explains how he protects them. In the same way, a class of older children can develop attitudes through discussion, research, outside reading and all-day trips. Finally, a teacher must constantly evaluate her own attitudes, because her influence can be negative if she has personal prejudices. This is especially true in respect to controversial issues and questions on which children should be encouraged to reach their own decision as a result of objective analysis of all the facts.

单选题当x分别取值时，计算代数式的值，将所得的结果相加，其和等于()．

单选题过抛物线y=ax2(a＞0)的焦点F作一直线交抛物线于P、Q两点，若线段PF与FQ的长分别是p、q，则等于______。A．2aB．C．4aD．

单选题已知(1+ax)7的展开式中，所有项的系数和为128，则a=( )．

单选题已知a，b，c互不相等，三个关于x的一元二次方程ax2+bx+c=0，bx2+cx+a=0，cx2+ax+b=0恰有一个公共实数根，则的值为______．

单选题曲线y=e x 与其过原点的切线及y轴所围面积为

单选题随机变量(X，Y)服从二维正态分布，其边缘分布为X～N(1，1)，Y～N(2，4)，X与Y的相关系数为ρXY=-0.5且概率PaX+bY≤1)=，则______．

单选题事件A与B互斥，他们都不是不可能事件，则下列结论：P(A＋B)=P(A)＋P(B)；P(A)≠0；0＜P(B)＜1；P(A)＞P(B)，其中正确的个数是 ( )

单选题曲线y=x2与曲线y=aln x(a≠O)相切，则a= A. 4e． B. 3e． C. 2e． D. e．

单选题The newly designed zoom has overcome distortion previously ______ in a zoom of this range. A. inherent B. genetic C. coherent D. generic