单选题设f(x)在区间(0，+∞)上可导，下列命题 ①若f(x)在(0，+∞)上无界，则f'(x)在(0，+∞)上有界． ②若f'(x)在(0，+∞)上无界，则f(x)在(0，+∞)上有界． ③若f(x)在(0，+∞)上无界，则f'(x)在(0，+∞)上无界． ④若f'(x)在(0，+∞)上无界，则f(x)在(0，+∞)上无界． 正确的个数 A.0个． B.1个． C.2个． D.至少3个．

单选题一项工程由甲、乙两队合做30天可完成．甲队单独做24天后，乙队加入，两队合做10天后，甲队调走，乙队继续做了17天才完成．若这项工程由甲队单独做，则需要( )． A．60天 B．70天 C．80天 D．90天 E．100天

单选题设那么与对角矩阵相似的矩阵是

单选题y"+2y'+y=e-x+1的特解具有形式

单选题已知随机向量(X1，X2)的概率密度为f1(x1，x2)，设则随机向量(Y1，Y2)的概率密度为f2(y1，y2)=______A．B．C．D．

单选题[2012年10月]一满桶纯酒精倒出10升后，加满水搅匀，再倒出4升后，再加满水。此时，桶中的纯酒精与水的体积之比是2：3。则该桶的容积是( )。

单选题设，则x=1为f(x)在[-2，2]上的

单选题When an associate of the Mus6e d'Art Moderne Andr6-Malraux in Normandy flipped through the catalogue for the auction of impressionist art at Sotheby's in New York on November 2nd, he made a startling discovery. On sale was "Blanchisseuses souffrant des dents", a painting by Edgar Degas, which had been stolen in 1973 from a museum where it had been on loan from the Louvre. After being alerted by the French authorities, Sotheby's dropped the painting from the sale. Now an investigation is under way. The owner is likely to lose it without compensation when it is returned to France. Like most art collectors, the owner had no art-title insurance, which would have provided compensation for the painting's value. "Theft accounts for only a quarter of title disputes," says Judith Pearson, a co-founder of ARIS, a small insurance firm that has been selling title insurance since 2006 and which was taken over by Argo Group, a bigger insurer, earlier this month. Three-quarters of squabbles occur in cases of divorce or inheritance. A work of art may also carry liens after being used as a collateral for a loan. More rarely, two or more artists may collaborate but then disagree about who has authority to flog their co-production. Does the risk of title disputes warrant the cost of title insurance? ARIS charges a one-off premium of between 1.75% and 6% of the art's value. In return the company will cover the legal costs in case of a title dispute and compensate for the agreed value of the art if their client loses the ownership dispute. ARIS has so far written about 1,000 policies and has not yet had a claim. An alternative to art-title insurance is for collectors to do due diligence about the provenance of a work of art themselves. Yet many do not have the time or the tools to carry out such research, which is a complex undertaking as there is no central register of art ownership. And even sophisticated collectors get it wrong, as the clients of Salander-O'Reilly, a New York art gallery, discovered. It collapsed spectacularly in 2007 after it emerged that it had dealt in stolen art and defrauded its clients in a Madoffian manner for years. Such cases are exceptional, but as the market booms and the value of art increases, more art lovers will look for additional assurances that their art is really theirs.

单选题累次积分可写成

单选题双曲线在点p0(x0，y0)处的切线及x=a(a为切线在x轴上的截距)所围图形的面积为A(右图中阴影部分)，则以下选项中正确的是{{U}}{{/U}}。A.x0越大，面积A越大B.面积A与x0无关，恒为常数C.x0越大，面积A越小D.面积A不是x0的单调函数

单选题已知OA为球O的半径，过OA的中点M且垂直于OA的平面截球面得到圆M，若圆M的面积为3π，则球O的表面积等于______A.4πB.6πC.8πD.12πE.16π

单选题曲线的拐点坐标为()A．(a，0)B．(a，-b)C．(a，b)D．(b，a)