单选题若函数f(x)=ln(3x)，则f"(2)等于______。A．6B．ln6C．D．

单选题设则在(-∞，+∞)内，下列正确的是______

单选题约等于几?

单选题已知A为三阶方阵，1，1，2是A的三个特征值，α 1 ，α 2 ，α 3 分别为对应的三个特征向量，则______

单选题设y=lnx，则y"=()

单选题从水平放置的球体容器的顶部的一个孔向球内以相同的速度注水．容器中水面的高度与注水时间t之间的关系用图像表示应为()．(E)以上均不正确

单选题A weather map is an important tool for geographers. A succession of three of four maps presents a continuous picture of weather changes. Weather forecasts are able to determine the speed of air masses and fronts; to determine whether an individual pressure area is deepening or becoming shallow and whether a front is increasing or decreasing in intensity. They are also able to determine whether an air mass is retaining its original characteristics or taking on those of the surface over which it is moving. Thus, a most significant function of the map is to reveal a synoptic picture of conditions in the atmosphere at a given time. All students of geography should be able to interpret a weather map accurately. Weather maps contain an enormous amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States weather Bureau issues information about approaching storms, floods, frosts, droughts, and all climatic conditions in general. Twice a month it issues a 30-day "outlook" which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an analysis of the upper air levels with often set the stage for the development of air masses, fronts, and storms. Considerable effort is being exerted today to achieve more accurate weather predictions. With the use of electronic instruments and earth satellites, enormous gains have taken place recently in identifying and tracking storms over regions which have but few meteorological stations. Extensive experiments are also in progress for weather modification studies. But the limitations of weather modification have prevented meteorological results except in the seeding of super-cooled, upslope mountainous winds which have produced additional orographical precipitation on the windward side of mountain ranges. Nevertheless, they have provided a clearer understanding of the fundamentals of weather elements.

单选题AB和CD为平面内两条相交直线，AB上有m个点，CD上有n个点，且两直线上各有一个与交点重合，则以这m+n-1个点为顶点的三角形的个数是()．

单选题长方体三条棱长分别为1，2，3，则该长方体的对角线的长为（　　）

单选题某班同学在一次英语测验中，平均成绩为81分，其中男生人数比女生人数多60%，而女生平均成绩比男生高10%，那么女生平均成绩为______。

单选题三阶矩阵A=()时，ζ=(-2，-1，2)T是AX=0的基础解系．

单选题设a是三角形的一个内角，若

单选题设γ1=(5，1，-5)T，γ2=(1，-3，2)T，γ3=(1，-2，1)T，Aγ1=(4，3)T，Aγ2=(7，-8)T，Aγ3=(5，-5)则A={{U}}{{/U}}．

单选题两个正数a，b(a＞b)的算术平均值是其几何平均值的2倍，则与最接近的整数是______．

单选题曲线|xy|+1=|x|+|y|所围成的图形的面积为______A．B．C．1D．2E．4

单选题设f(x)为连续函数，且，则曲线y=f(x)在x=2处切线方程为()。A．y=x-5B．y=2x-7C．y=x+5D．y=2x+7

单选题三角形的三边长为2，x，9，x为奇数，则周长为{{U}} {{/U}}． A.18 B.19 C.20 D.21

单选题圆x2+y2+2x-6y-6=0的半径为（　）

单选题The first two assumptions made about the ______ of TV were dead wrong: that it would bury radio and it would be a threat to movies. A. recession B. advent C. diversity D. bias