阅读下面文章，完成下列小题。

　　①鸟儿在空中飞翔时，翅膀每分钟拍几次？每次幅度有多大？鱼儿在水里游动时，尾巴每分钟摆几回？每回幅度又是多少？这些问题看上去似乎没什么意义，难道空中的飞鸟和水里的游鱼不是完全自由的吗？它们的运动不是完全无拘无柬的吗？     

　　②答案真是出乎我们的意料。看上去自由自在、无拘无束的飞行动物和游水动物，它们的运动似乎恰恰遵循着严格的规律。科学家们通过大量的观察和实验，发现飞行动物和游水动物的运动过程中存在着一个神秘的常数，那就是它们的翅膀和尾巴的振动频率、振幅以及运动速度三者之间的关系——振动频率乘以振幅再除以运动速度，计算得到的数值总是落在0. 2～0.4之间。  

　　③比如，世界上最小的鸟类——蜂乌，其双翅展开仅有10厘米左右，飞翔时振幅大约是20厘米。蜂鸟飞行速度非常快，大约能达到50米／秒。而科学家们以往观察到的蜂鸟飞行时双翅振动频率在50～70赫兹之间，根据上述公式计算出来的蜂鸟的运动常数就落在0. 2～0.4之间。  

　　④与蜂鸟形体相差悬殊的海豚也是科学家们观察的一个对象。成年海豚的体长一般在3米左右，在大海里游劫时，海豚尾巴摆动的振幅大约是1米，频率每分钟30次左右，游动速度是每小时100公里。根据公式计算出来的海豚的运动常数是0.3，也落在0.2～0.4之间。  

　　⑤这不仅仅是巧合，研究者们做了大量的试验，发现几乎所用的飞行动物和游水动物的运动机制中都存在着这个神秘的常数。事实上，只有当这一运动常数的值处于0.2～0.4之间，动物们才能达到最佳的运动状态。

　　⑥虽然目前科学家们还不清楚为什么会存在这个运动常数，它的值又为什么恰恰落在0. 2～0.4之间，但这一神奇常数似乎像物理学中著名的光速不变原理那样放之四海而皆准，也像光速一样神秘。它能够帮助生物学家们根据动物化石的身体构造，判断出那些早已灭绝了的动物曾经具有怎样的运动速度。甚至，不能排除，这一常数很可能对外星生物也同样适用。很多科学家都表示：“如果在其他星球上真的存在飞行生物或游水生物的话，我们相信，它们的运动也遵循着同样的规律。”     

　　⑦此外，这一常数还能够帮助军方研制出各种高性能的飞行器。比如说，一个翼长15厘米、翼振振幅为10厘米的机械间谍如果要做有效飞行的话，其最佳翼振频率应该是 30次／秒左右。目前美国军方已经着手研制类似于飞鸟的有翼飞行器，在酤备上微型摄像机之后，这样的机械鸟可能渗入敌方的任何机密要塞进行刺探。当然，他们最感兴趣的还是能够研制出体积更小、无孔不入的机械昆虫，相信这一天的到来也为时不晚。

1．下列理解和分析不符合原文意思的一项是（     ）   

A．本文是一篇事理说明文，是按照逻辑顺序说明的。   

B．科学研究表明，空中的飞鸟和水中的游鱼的运动并不完全是白由的。   

C．海豚的形体要比蜂鸟大得多，但它们的运动常数却都落在0.2～0.4之间。   

D．美国军方研制m的机械鸟可能渗入敌方的机密要塞进行刺探。

2．第③④两段运用_______，_______的说明方法，说明了_______。

3．第⑤段中加粗词“不仅仅”能否删去？为什么？

答：＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿。

4．神秘的“运动常数”在目前的科学研究中，具有怎样的用途？

答：________________________________________。

An American educational expert, Frederick M. Hess, says that a long summer vacation doesn’t make sense in today’s world.

This summer, 50 million kids will spend much time talking online, watching TV, playing video games and asking older brothers or sisters to take them to the supermarket. They will also be putting their academic futures at risk.

During much of the 20th century, many Americans worked in factories that did not need a college degree but still offered a high salary. Also, in the 19th century, there was no air condition. And poor hygiene (卫生) meant that crowded schools had health risks.

Things have changed. For today’s students, academic skills are key to future success. Many countries don’t give kids an American-style summer vacation. They offer no more than seven consecutive (连续的) weeks of vacation. Most American school districts offer up to 13 weeks. To compete in global marketplace, Americans must be prepared to go up against international competitors.

Summer vacation also causes challenges for today’s families. In the 1960s, more than 60% of families had a stay-at-home mum. Now, two-thirds of American children live families where every adult works. For these families, summer vacation can be more burden than break. Someone must watch the kids.

But the biggest problem may be how summer vacation hurts academic achievement. Scientist have found that disadvantaged students lose important ground in the summertime.

A school year can allow time-limited teachers to conduct richer and more imaginative lessons. Schools would have more time for sports, languages, music and the arts.

小题1:Before the 20th century, a long summer vacation might ______.

A．reduce income for Americans

B．reduce health risks for students

C．cause career failure for Americans

D．cause loss in global market for America小题2: How long does an American-style summer vacation last？

A．No more than two months.

B．Less than three months.

C．As long as three months.

D．As long as four months.小题3:According to the text, who will benefit from a long school year?

A．American students, teachers and parents.

B．American students, parents and shop owners.

C．American students, parents and international competitors.

D．American students, teachers and international competitors.小题4:How many reasons did the writer give to support his/her opinion?

A．One.

B．Two.

C．Three.

D．Four.