设L为椭圆，其周长为a，求曲线积分．

当你在花园里驻足观察那些胖胖的蜜蜂在花丛中起起落落，或者在厨房手拿苍蝇拍对着狡猾的苍蝇无可奈何时，你一定认同以下观点：把“飞行家”这个名词冠于昆虫身上是恰如其分的，昆虫不仅是地球上规模最大的飞行家族，也是最早掌握这项技术的先驱者。地球上的第一次飞行是个什么场景？这一历史性的是时刻早已消失在岩层之中。不过，当年第一批飞行者的后代仍然活跃在我们的星球上，他们就是蜉蝣。　　蜉蝣这种生物大多数时间生活在水中，以藻类为食，当它们准备好繁殖，便爬出水面，在水边的植物上蜕皮，成为有翅的成虫。这些获得新生的小虫子并不急于飞行，多数时候会聚集在水面上，伸展双翅，在微风的吹拂下于水面上滑行。当时机成熟，便风中舞动，在空中完成婚配。不久，雌虫产卵，刚刚脱离水面不过几十小时的蜉蝣们再次回落水中，这也意味着它们个体生命的终结。目前，多数昆虫学家认为，最早的昆虫也像蜉蝣一样，是从水面滑行演化到飞行的，最早的翅应该是“风帆”，而非“机翼”。昆虫的翅是一个工程学奇迹：一片几丁质的薄层，没有任何骨骼和肌肉的支撑。几丁质这种物质本身柔软而坚韧，就连碳纤维复合材料都无法与之相比。几丁质中贯穿着翅脉，它们是液压管道，正是这些液压管道让昆虫的翅膀有了足够的刚性来应对飞行时巨大的应力考验。与鸟、蝙蝠的翅膀一样，昆虫翅膀的剖面上端弯曲，下端平直，这使得空气流过翼面时产生升力。昆虫与其他任何飞行动物的标志性区别，在于它们扇动翅膀时高得惊人的速度——蜻蜓一般为每秒200次，而蚊子和马蜂则能高达每秒1000次。不仅如此，如果逐格回放高速摄像机拍摄的昆虫飞行影像，你会惊奇地发现，昆虫扑翼飞行可不简单是上下运动，从侧面观察，昆虫的翅膀其实是在画八字形。直到最近，人们把昆虫放进风洞好好研究了一番才发现，其实这些小家伙的翅膀是在空气中制造涡流，依靠这些可控的涡流，它们的翅膀在向下和向上拍动时都能产生升力，这是鸟与蝙蝠绝对无法做到的，一只小蜜蜂借助这些涡流，产生达到其体重3倍的开力，而向前的推力则是体重的8倍之多，与之相比，一架战斗机的推力与重力大小之比能达到2就可以“笑傲江湖”了，这样你就不难理解，为什么苍蝇能在空中做出令人匪夷所思的急转弯了。当然，这一切代价也相当高昂，飞行是件十分费力的活儿，一只果蝇飞行1小时就要消耗掉体重的10%，果蝇使用碳水化合物作为动力来源，这有点不太划算，其他很多昆虫直接利用脂肪作为“燃烧”，便让飞行的“经济性”大为改观。所以你绝对不能小看昆虫的能力，一只小小的黑脉金斑蝶能以每天150公里的速度连续飞行3000公里，完成从北美到中美洲的长途迁徙。 （取材于王冬《御风飞行》）

下列对文章内容理解和分析。不恰当的两项是（4分）

A．昆虫最初驾驭“风帆”在水面上滑行。后来逐步从滑行演变到在空中飞行。

B．蜉蝣有翅后即升空飞行。虽然飞行时间不长，但由此实现了生命的延续。

C．昆虫翅膀的剖面，上端弯曲，下端平直，这可以使空气滤过翼面时产生升力。

D．昆虫利用碳水化合物和脂肪作为“燃料”，从而大大提高了飞行的“经济性”。

E．昆虫是地球上规模最为庞大的飞行家族，很多昆虫都具有长途迁徙的能力。

下列哪项不属于生物的基本特征[ ]

A．能排出身体内产生的废物

B．能对外界刺激作出反应

C．能生长和繁殖

D．能进行光合作用

我国仍处于并将长期处于社会主义初级阶段。下列对社会主义初级阶段的认识正确的是[     ]

A．它仅表现于经济方面

B．它是我国的基本国情

C．就是不发达阶段

D．从建国算起，至少需要一百年时间

The collapse of Enron, the largest bankruptcy in American history, has rung out a banner year for American business failures. In Europe, the fallout from the Swissair and Sabena insolvencies continues. In the current global slump, more companies are likely to go under. Now is a perfect time to reconsider how to handle such failures: let them sink, or give them a chance to swim

In America, bankruptcy has come to mean a second chance for bust businesses. The famous "Chapter 11" law aims to give a company time to get back on its feet, by shielding it from debt payments and prodding banks to negotiate with their debtor. It even allows an insolvent company to receive fresh finance after it goes bust. On the other side of the Atlantic, when companies stumble, almost as much effort is spent in fingering the guilty as in trying to salvage a viable business. British and French laws, for example, can make a failing company’s directors face criminal penalties and personal liability. Moreover, bankers have the power, at the first sign of trouble, to push a company into the arms of the receivers. Some modest changes are afoot, however. Britain is considering moves that would bring its rules closer to America’s. New laws in Germany should also make it easier to revive sick companies, although trade unions still have their say.

But even with the arrival of the euro and moves towards a single financial market, going bust in Europe is a strictly local affair. Long before America had a single currency, the American constitution provided uniform bankruptcy laws, observes Elizabeth Warren of the Harvard Law School. Europe’s patchwork of national laws, according to Bill Brandt of " Development Specialists", a consultancy, inhibits lending and makes it difficult to fix ailing firms.

Transatlantic insolvencies are even harder, as a Belgian-based software company, Lernout and Hauspie, discovered this year. Its American reorganization plan was thwarted by a Belgian judge, who ordered a sale of the firm’s assets. As the European Union inches toward greater harmonization, should it try to mimic America

Critics of Chapter 11 think not. They argue that America’s bankruptcy system is wasteful, lets failed managers go unpunished, and gives some companies an unfair advantage. In Chapter 11, admittedly, lawyers and advisers gobble up fees, but a recent study argues that the fees are no larger than those for most mergers and acquisitions. One common complaint, that managers enjoy the high life while creditors go begging, fails to stand up to the data from America’s previous wave of bankruptcies in the early 1990s. Stuart Gilson of the Harvard Business School found that more than two-thirds of top managers were ousted within two years of a bankruptcy filing. More troubling is that some American firms seem to enjoy second and third trips to bankruptcy court, cheekily termed Chapters 22 and 33. Some see this as evidence that, ton often, they use Chapter 11 to keep running. But there is more to the story.

The last paragraph is mainly（）

A. to accuse the lawyers and advisers of making big money by helping those insolvent companies

B. to introduce the changes of the bankruptcy law—Chapter 11

C. to prove the accusation is groundless that the managers of bust businesses lead a comfortable life at the cost of creditors

D. to argue that the European Union should not follow the American example in their effort to revive sick companies

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