单选题某工厂生产某种定型产品，一月份每件产品销售的利润是出厂价的25%(假设利润等于出厂价减去成本)．若二月份每件产品的出厂价降低10%，成本不变，销售件数比一月份增加80%，那么二月份的销售总利润比一月份的销售总利润增长______．

单选题从甲地到乙地，水路比公路近40千米，上午10:00，一艘轮船从甲地驶往乙地，下午1:00，一辆汽车从甲地开往乙地，最后船、车同时到达乙地．若汽车的速度是每小时40千米，轮船的速度是汽车的，则甲乙两地的公路长为______．

单选题设函数f(x)在区间[-1，1]上连续，则x=0是函数的______．A．跳跃间断点B．可去间断点C．无穷间断点D．振荡间断点

单选题方程x 2 -2006|x|=2007所有实数根的和等于______．

单选题函数f(x)=x sin x

单选题设f'x(x0，y0)，f'y(x0，y0)都存在，则

单选题若对一切正实数x恒成立，则y的取值范围是______．

单选题A．0．B．不存在．C．D．

单选题The marvelous telephone and television network that has now enmeshed the whole world, making all men neighbors, cannot be extended into space. It will never be possible to converse with anyone on another planet. Even with today's radio equipment, the messages will take minutes—sometimes hours—on their journey, because radio and light waves travel at the same limited speed of 186, 000 miles a second. Twenty years from now you will be able to listen to a friend on Mars, but the words you hear will have left his mouth at least three minutes earlier, and your reply will take a corresponding time to reach him. In such circumstances, an exchange of verbal messages is possible—but not a conversation. To a culture which has come to take instantaneous communication for granted, as part of the very structure of civilized life, this "time barrier" may have a profound psychological impact. It will be a perpetual reminder of universal laws and limitations against which not all our technology can ever prevail. For it seems as certain as anything can be that no signal--still less any material object—can ever travel faster than light. The velocity of light is the ultimate speed limit, being part of the very, structure of space and time. Within the narrow confines of the solar system, it will not handicap us too severely. At the worst, these will amount to twenty hours—the time it takes a radio signal to span the orbit of Pluto, the outer-most planet. It is when we move out beyond the confines of the solar system that we come face to face with an altogether new order of cosmic reality. Even today, many otherwise educated men—like those savages who can count to three but lump together all numbers beyond four—cannot grasp the profound distinction between solar and stellar space. The first is the space enclosing our neighboring worlds, the planets; the second is that which embraces those distant suns, the stars, and it is literally millions of times greater. There is no such abrupt change of scale in the terrestrial affairs. Many conservative scientists, appalled by these cosmic gulfs, have denied that they can ever be crossed. Some people never learn ; those who sixty years ago scoffed at the possibility of flight, and ten years ago laughed at the idea of travel to the planets, are now quite sure that the stars will always be beyond our reach. And again they are wrong, for they have failed to grasp the great lesson of our age— that if something is possible in theory, and no fundamental scientific laws oppose its realization, then sooner or later it will be achieved. One day we shall discover a really efficient means of propelling our space vehicles. Every technical device is always developed to its limit and the ultimate speed for spaceships is the velocity of light. They will never reach that goal, but they will get very near it. And then the nearest star will be less than five years voyaging from the earth.

单选题在一个101人参加的聚会上，下列结论正确的是______

单选题设y=2x2-lny，则y"=A．B．C．D．

单选题=()A．0B．C．D．1

单选题函数，以f(x)表示f(3x)为______。A．B．C．D．

单选题用A表示事件“甲考核通过且乙考核不通过”，则其对立事件A为

单选题设随机变量X服从[-1，1]上的均匀分布，则X与Y=e-|X|______。 A．不相关 B．相关 C．独立 D．相关且不独立

单选题过点A(2，0)向圆x2+y2=1作两条切线AM和AN，(如图6-59)，则两切线与圆所围成的图形面积(图中阴影部分)为()．

单选题一个游泳池，甲管放满水需6小时，甲、乙两管同时放水，放满需4小时。如果只用乙管放水，则放满需______

单选题设函数f(x)在[0，1]上连续，令t=x+1，则等于______。A．B．C．D．

单选题曲线y=x 2 与曲线y=alnx(a≠0)相切，则a=

单选题将函数展成x的幂级数．