单选题设矩阵，已知矩阵A相似于B，则秩(A-2E与秩(A-E)的和等于()．

单选题设函数，则f(y，x)等于______。A．B．C．D．

单选题When older people can no longer remember names at a cocktail party, they tend to think that their brainpower is declining. But a growing number of studies suggest that this assumption is often wrong. Instead, the research finds, the aging brain is simply taking in more data and trying to sift through a clutter of information, often to its long-term benefit. The studies are analyzed in a new edition of a neurology book, "Progress in Brain Research. " Some brains do deteriorate with age. Alzheimer's disease, for example, strikes 13 percent of Americans 65 and older. But for most aging adults, the authors say, much of what occurs is a gradually widening focus of attention that makes it more difficult to latch onto just one fact, like a name or a telephone number. Although that can be frustrating, it is often useful. "It may be that distractibility is not, in fact, a bad thing," said Shelley H. Carson, a psychology researcher at Harvard whose work was cited in the book. "It may increase the amount of information available to the conscious mind. " For example, in studies where subjects are asked to read passages that are interrupted with unexpected words or phrases, adults 60 and older work much more slowly than college students. Although the students plow through the texts at a consistent speed regardless of what the out-of-place words mean, older people slow down even more when the words are related to the topic at hand. That indicates that they are not just stumbling over the extra information, but are taking it in and processing it. When both groups were later asked questions for which the out-of-place words might be answers, the older adults responded much better than the students. "For the young people, it's as if the distraction never happened," said an author of the review, Lynn Hasher, a professor of psychology at the University of Toronto and a senior scientist at the Rotman Research Institute. "But for older adults, because they've retained all this extra data, they' re now suddenly the better problem solvers. They can transfer the information they've soaked up from one situation to another. " Such tendencies can yield big advantages in the real world, where it is not always clear what information is important, or will become important. A seemingly irrelevant point or suggestion in a memo can take on new meaning if the original plan changes. Or extra details that stole your attention, like others'yawning and fidgeting, may help you assess the speaker's real impact.

单选题设集合M={x||x—2|2}，则M∩N=(　　)

单选题下列函数f(x)中，导函数f"(x)在x=0处不连续的是A．B．C．D．

单选题已知多项式2x4-3x3-ax2+7x+b能被x2+x-2整除，则=()．

单选题当x→0时，下列函数以零为极限的是()。

单选题设，则x=1为f(x)在[-2，2]上的____

单选题设f(x)是奇函数，其中a为不等于1的正数，则F(x)是{{U}}{{/U}}。A.偶函数B.奇函数C.非奇非偶函数D.奇偶性与a有关

单选题给出以下三个二次型，①②③正定二次型的个数为()．

单选题数列中的最大项n为

单选题甲、乙两人上午8:00分别从A、B出发相向而行，9:00第一次相遇，之后速度均提高了1.5公里/小时，甲到B，乙到A后都立刻沿原路返回，若两人在10:30第二次相遇，则A、B两地的距离为______．

单选题设函数f(x)在[a，b]上连续，则下列结论不正确的是( )

单选题极限____

单选题设函数，则fy(1，0)等于______．

单选题直线l与x轴平行，且与曲线y=x-e x 相切，则切点的坐标为______。

单选题设矩阵B的列向量线性无关，且BA=C，则( )

单选题设y=x -2 +3，则y"| x=1 =______．

单选题设则n=

单选题设，其中D={(x，y)|(x-1)2+(y-1)2≤2}，则______