单选题两个码头相距198km，如果一艘客轮顺流而下行完全程需要6h，逆流而上行完全程需要9h，那么该艘客轮的航速和这条河的水流速度分别是( )km/h． A．27.5和5.5 B．27.5和11 C．26.4和5.5 D．26.4和11

单选题"High tech" and "state of the art" are two expressions that describe very modern technology. High tech is just a shorter way of saying high technology. And high technology describes any invention, system of device that uses the newest ideas or discoveries of science and engineering. What is high tech? A computer is high tech. So is a communications satellite. A modern manufacturing system is surely high tech. High tech became a popular expression in the United States during the early 1980's. Because of improvements in technology, people could buy many new kinds of products in American stores, such as home computers, microwave ovens, etc. "State of the art" is something that is as modern as possible. It is a product that is based on the very latest methods and techn01ogy. Something that is "state of the art" is the newest possible design or product of a business or industry. A state of the art television set, for example, uses the most modern electronic design and parts. It is the best that one can buy. "State of the art" is not a new expression. Engineers have used it for years, to describe the best and most modern way of doing something. Millions of Americans began to use the expression in the late 1970's. The reason was the computer revolution. Every computer company claimed that its computers were "state of the art". Computer technology changed so fast that a state of the art computer today might be old tomorrow. The expression "state of the art" became as common and popular as computers themselves. Now all kinds of products are said to be "state of the art".

单选题若从原点出发的质点M向x轴的正向移动一个和两个坐标单位的概率分别是和，则该质点移动3个坐标单位，到达x=3的概率是______A．B．C．D．E．

单选题在△ABC中，AB=10，AC=8，BC=6，过C点以C到AB的距离为直径作圆，该圆与AB有公共点，且交AC于M，交BC于N，则MN等于______。A．B．C．D．

单选题差分方程y t -2y t-1 =b(b为常数)的通解是______．

单选题设n阶矩阵A的行列式|A|=a≠0(n≥2)，λ是A的一个特征值，A * 为A的伴随矩阵

单选题甲、乙两组射手打靶，两组射手的平均成绩是150环。(1)甲组的人数比乙组人数多20％。(2)乙组的平均成绩是171．6环，比甲组的平均成绩高30％。

单选题A是4阶矩阵，设A=(α1，α2，α3，α4)，其中向量组α2，α3，α4线性无关，且α1-3α2-2α3，则齐次线性方程组AX=0______。 A．有非零解，且通解为X=k(1，-3，2，0)T(k为任意实数) B．有非零解，且通解为X=k(1，-3，-2)T(k为任意实数) C．有非零解，且通解为X=k(1，-2，3，1)T(k为任意实数) D．只有零解

单选题如下图所示，一个底面半径为R的圆柱形量杯中装有适量的水．若放入一个半径为r的实心铁球，水面高度恰好升高r，则A．B．C．D．E．

单选题微分方程y"-7y'+12y=0的通解是( )。A．y=Ce3xB．y=Ce4xC．y=e3x(C1cos 4x+C2sin 4x)D．y=C1e3x+C2e4x

单选题设f(x)可导，且F(x)=f(x)(1+|sinx|)在x=0处可导，则______.

单选题[2011年1月]现有一批文字材料需要打印，两台新打印机单独完成此任务分别需要4小时与5小时，两台旧型打印机单独完成任务分别需要9小时与11小时。则能在2．5小时内完成此任务。 (1)安排两台新型打印机同时打印： (2)安排一台新型打印机与两台旧型打印机同时打印。