单选题设y=y(x)是初值问题的解，则______A．x=1是y(x)的极大值点，且极限B．x=1是y(x)的极大值点，且极限C．x=1是y(x)的极小值点，且极限D．x=1是否为y(x)的极值点与参数a有关，且极限

单选题船航行每小时的费用由两个部分组成．日常开销(固定部分)为k1，燃油费(变动部分)与速度立方成正比，比例系数k2＞0．在航程确定的情况下，使船航行总费用最小的航速为A．B．C．D．

单选题当x→1时，函数的极限

单选题设下述命题成立的是()．

单选题设函数y=f(x)由方程cosxy+lny-x=1确定，则

单选题设f(x)在[a，+∞)连续，则“”是f(x)在[a，+∞)无界的

单选题Globally, recovery is going slightly better than expected, according to the IMF, which released its latest World Economic Outlook today. After shrinking by 0.6% last year, the global economy is likely to expand by 4.2% in 2010, 0.3% faster than the IMF projected in January. But economic performances will continue to vary widely around the world. Much of the upward revision to global growth can be attributed to a better outlook for the American economy. The IMF revised its forecast for American economic expansion in 2010 up 0.4%, to 3.1%. There was no change, by contrast, for the euro area, which already faced a poorer growth outlook. The Euro area economy may only grow by 1% in 2010 and 1.5% in 2011. And much of the job of expansion will be handled by Germany and France, while southern European growth continues to lag. Spain's economy will continue to shrink in 2010. But the outlook is brightening for many emerging economies, including those in central and eastern Europe, for which growth forecasts were revised up by 0.8%. Developing Asia is enjoying a strong recovery, and the IMF indicated that both India and Brazil are likely to perform much better this year than initially anticipated, notching (赢得) growth rates of 8.8% and 5.5%, respectively. The report suggested that planned stimulus measures for 2010 should be fully implemented, given the fragility of recovery, but it also noted that sovereign debt worries will become more severe as the year progresses. Debt issues are likely to prove especially problematic in Europe, which has the highest debt ratios and the slowest expected growth rates. The stressed southern European nations are in a damned-if-they-do-damned-if-they-don't position. If little action is taken on debt, rising debt costs will choke of an already weak recovery. If aggressive action is taken, the blow to aggregate demand will likewise undermine growth. Around the world, trade and production have recovered strongly, but employment remains well below prerecession levels in most countries. Labour market weakness is helping to keep inflation expectations in check; the IMF forecasts consumer price increases in developed nations of 1.5% in 2010 and 1.4% in 2011. But the return to strong growth is boosting commodity prices once more. Oil prices may increase by 30% in 2010, said the IMF, a rise 7% larger than projected in January. The overall picture is of a remarkable turnaround in global fortunes, given the depth of the recession. The year's performance is much better than many would have dared to hope early last year. But in parts of Europe, the future is somewhat less certain, and because that uncertain future could lead to sovereign debt crises that could potentially rattle financial markets, world leaders should remain vigilant.

单选题设且f(n)(x)在点x=0处连续，则n的最大值是

单选题设A，B及A*都是n(n≥3)阶非零矩阵，且AB=O，则r(B)=______．

单选题设，其中f(x)在x=0处可导，f'(0)≠0，f(0)=0，则x=0是F(x)的______．A．连续点B．可去间断点C．跳跃间断点D．第二类间断点