单选题在△ABC中，∠BAC=∠ABC=45°，点P在AB上，AD⊥CP，BE⊥CP，垂足分别为D、E，已知DC=2，则BE=( )．

单选题设f（x）的一个原函数为cos2x，则f（x）=

单选题You really do have to wonder whether a few years from now we'll look back at the first decade of the 21st century—when food prices spiked, energy prices soared, world population surged, tornados plowed through cities, floods and droughts set records, populations were displaced and governments were threatened by the confluence of it all—and ask ourselves. What were we thinking? How did we not panic when the evidence was so obvious that we'd crossed some growth, climate, natural resource and population redlines all at once? "The only answer can be denial," argues Paul Gilding, an Australian environmentalist, in a new book called The Great Disruption. "When you are surrounded by something so big that requires you to change everything about the way you think and see the world, then denial is the natural response. But the longer we wait, the bigger the response required." Gilding cites the work of the Global Footprint Network, an alliance of scientists, which calculates how many "planet Earths" we need to sustain our current growth rates. G. F. N. measures how much land and water area we need to produce the resources we consume and absorb our waste, using prevailing technology. On the whole, says G. F. N. , we are currently growing at a rate that is using up the Earth's resources far faster than they can be sustainably replenished, so we are eating into the future. This is not science fiction. This is what happens when our system of growth and the system of nature hit the wall at once. We are now using so many resources and putting out so much waste into the Earth that we have reached some kind of limit, given current technologies. The economy is going to have to get smaller in terms of physical impact. We will not change systems, though, without a crisis. But don't worry, we're getting there. We're currently caught in two loops: One is that more population growth and more global warming together are pushing up food prices, causing political instability in the Middle East, which leads to higher oil prices, thus to higher food prices and more instability. At the same time, improved productivity means fewer people are needed in every factory to produce more stuff. So if we want to have more jobs, we need more factories. More factories making more stuff make more global warming, and that is where the two loops meet. But Gilding is actually an eco-optimist. As the impact o the imminent Great Disruption hits us, he says, "our response will be proportionally dramatic, mobilizing as we do in war. We will change at a scale and speed we can barely imagine today, completely transforming our economy, including our energy and transport industries, in just a few short decades. " We will realize, he predicts, that the consumer-driven growth model is broken and we have to move to a more happiness-driven growth model, based on people working less and owning less.

单选题如图，面积为9平方厘米的正方形EFGH在面积为25平方厘米的正方形ABCD所在平面上移动，始终保持EF//AB，记线CF的中点为M，DH的中点为N，则线段MN的长度是()厘米．

单选题设2 a =3，2 b =6，2 c =12，那么a，b，c______．

单选题关于，下列结论正确的是

单选题设在全平面上有则使得f(x1，y1)＜f(x2，y2)成立的一个充分条件是

单选题设f(x)为可导函数，则(∫f(x)dx)"为______。

单选题设A是4阶方阵，则下列线性方程组是同解方程组的是______

单选题已知A，B均是三阶矩阵，将A中第3行的-2倍加至第2行得到矩阵A1，将B中第2列加至第1列得到矩阵B1，又知，则AB=A．B．C．D．

单选题已知函数在上连续，设，则交换积分次序后 (   )

单选题设三阶矩阵A的特征值是0，1，-1，则下列命题中不正确的是

单选题函数f(x)=cosx+xsinx在(-2π，2π)内的零点个数为

单选题设幂级数的收敛半径分别为，则幂级数的收敛半径为______．

单选题某年级60名学生中，有30人参加合唱团，45人参加运动队，其中参加合唱团而未参加运动队的有8人，则参加运动队而未参加合唱团的有______．

单选题设随机变量X服从参数为1的指数分布，则随机变量Y=min(X，2)的分布函数( )

单选题完成某项任务，甲单独做需4天，乙单独做需6天，丙单独做需8天．现甲、乙、丙三人依次一日一轮换地工作，则完成该项任务共需的天数为______．A．B．C．6D．E．4

单选题连续独立地投两次硬币，令A 1 ={第一次出现正面}，A 2 ={第二次出现正面}，A 3 ={两次中一次正面一次反面}，A 4 ={两次都出现正面}，则______．

单选题∫cos(5-x)dx=______．A．sin(5-x)+CB．C．-sin(5-x)+CD．

单选题设n阶矩阵A非奇异(n≥2)，A*是矩阵A的伴随矩阵，则______．