还有一篇小行星的，早上出门前刚看到更新，特此感谢狗狗主人！ Yet the rubble-pile hypothesis is conceptually troublesome. The material strength of an asteroid is nearly zero, and gravity is so low you are tempted to neglect that, too. What’s left? The truth is that neither strength nor gravity can be ignored. Paltry though it may be, gravity binds a rubble pile together. And anyone who builds sand castles knows that even loose debris can cohere. Oft-ignored details of motion begin to matter: sliding friction, chemical bonding, damping of kinetic energy, electrostatic attraction and so on. (In fact, charged particles from the sun can cause dust at the surface to levitate.) We are just beginning to fathom the subtle interplay of these minuscule forces.
The size of an asteroid should determine which force dominates. One indication is the observed pattern of asteroidal rotation rates. Some collisions cause an asteroid to spin faster; others slow it down. If asteroids are monolithic rocks undergoing random collisions, a graph of their rotation rates should show a bell-shaped distribution with a statistical “tail” of very fast rotators. If nearly all asteroids are rubble piles, however, this tail would be missing, because any rubble pile spinning faster than once every two or three hours (depending on its bulk density) would fly apart. Alan Harris of the Jet Propulsion Laboratory in Pasadena, Calif., Petr Pravec of the Academy of Sciences of the Czech Republic in Prague and their colleagues have discovered that all but five observed asteroids obey a strict rotation limit [see illustration on page 48]. The exceptions are all smaller than about 150 meters in diameter, with an abrupt cutoff for asteroids larger than about 200 meters.
The evident conclusion—that asteroids larger than 200 meters across are multicomponent structures or rubble piles—agrees with recent computer modeling of collisions, which also finds a transition at that diameter. A collision can blast a large asteroid to bits, but those bits will usually be moving slower than their mutual escape velocity (which, as a rule of thumb, is about one meter per second, per kilometer of radius). Over several hours, gravity will reassemble all but the fastest pieces into a rubble pile [see illustration above]. Because collisions among asteroids are relatively frequent, most large bodies have already suffered this fate. Conversely, most small asteroids should be monolithic, because impact fragments easily escape their feeble gravity.
LZ做到的只有后2段，一个问文章的主要目的，一个问文章的结构，一个问削弱最后一段的第一句里的evident的。还有一个，绕了一大圈，问那些旋转的速度快得足以让行星fly apart的小行星一定是以下哪一种（囧，表达不能）。LZ的思路是这样的：If nearly all asteroids are rubble piles, however, this tail would be missing, because any rubble pile spinning faster than once every two or three hours (depending on its bulk density) would fly apart.因为行星们都不能旋转太快，否则他们会fly apart，又Alan Harris of the Jet Propulsion Laboratory in Pasadena, Calif., Petr Pravec of the Academy of Sciences of the Czech Republic in Prague and their colleagues have discovered that all but five observed asteroids obey a strict rotation limit。 The exceptions are all smaller than about 150 meters in diameter, with an abrupt cutoff for asteroids larger than about 200 meters. 所以，那些旋转得那么快，又不会fly apart的，就是那些BUT FIVE，既那些exceptions了，所以选smaller than about 150 meters in diameter 应该没错吧，还是请N人确定一下。
还有一个说，在某湖监测到了一个medical神马东东的存在，这种东东对人体有害，但是它的含量在一个很低的不会影响喝这些水的人的健康的数值。however，消除这个东东还是有必要的，因为消除这个东东对人的健康还是有好处的，问加强。LZ选了一个XX bacteria expose to 那个medical东东会变得对那个东东有抗体/抵抗力？= =LZ表达不能，大家自己体会。。。
坐稳 一个说L钢琴制造商以生产高质量昂贵的钢琴出名，但是最近L的revenue下降了。另一家乐器制造商A在引进了电子琴生产线之后，revenue增加，所以L也应该引进电子琴生产线in a variety of ranges，这样就能增加revenue甚至outsell A公司。又说customer会accept这些电子琴，因为customer会associate with L家的prestigious XX（品牌）？？
Which of the following most logically completes the passage? Using new detection techniques, researchers have found trace amounts of various medicinal substances in lakes and rivers. Taken in large quantities, these substances could have serious health effects, but they are present in quantities far too low to cause any physiological response in people who drink the water or bathe in it. Nevertheless, medical experts contend that eliminating these trace amounts from the water will have public health benefits, since __________. A. some of the medicinal substances found in lakes and rivers are harmless to humans even if taken in large quantities B. some of the medicinal substances found in lakes and rivers can counteract possible harmful effects of other such substances found there C. people who develop undesirable side effects when being treated with medicines that contain these substances generally have their treatment changed D. most medicinal substances that reach lakes or rivers rapidly break down into harmless substances E. disease-causing bacteria exposed to low concentrations of certain medicinal substances can become resistant to them（Answer）作者: 米米喵 时间: 2010-11-6 12:22
是这个没错~