单选题设级数收敛，则

单选题下列四项中正确的是()。

单选题设a=20，b=(-3)2，则a，b，c，d按由小到大的顺序排列正确的是()．

单选题等比数列{an}的前n项和为Sn，已知S1，2S2，3S3成等差数列，则{an}的公比为______A．2B．C．D．3E．

单选题从分别写有数字1，2，3，4，5的5张卡片中任意取出两张，把第一张卡片上的数字作为十位数字，第二张卡片上的数字作为个位数字，组成一个两位数，则所组成的数是3的倍数的概率是()．

单选题设f(x)在[0，+∞)上连续，在(0，+∞)内可导，则______．A．B．C．D．

单选题点(0，1)是曲线y=x 3 +bx 2 +c的拐点，则______

单选题某人下午三点钟出门赴约，若他每分钟走60米，会迟到5分钟，若他每分钟走75米，会提前4分钟到达．所定的约会时间是下午( )．

单选题某种产品有2只次品和3只正品，每只产品均不相同，今每次取出一只测试，直到2只次品全部测出为止，则最后一只次品恰好在第4次测试时发现的不同情况种数是______．

单选题设函数在x=0处极限存在，则a=()．

单选题若一个长方体的表面积是22cm2，所有棱长之和为24cm，则长方体的体对角线长为()cm。

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______