OG11紫皮 第11篇meteor stream 第61题

A meteor stream (meteor stream: 流星群) is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on (gain on: v.逼近, 超过, 侵蚀) or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles’ individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation (computer simulation: 计算机模拟) of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower (meteor shower: n.[天]流星雨) occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled “pipe” and one as it exited. There is no reason why the Earth should always pass through the stream’s exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 show just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.

61.

The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?

(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the steam.

(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.

(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.

(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.（D）

(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

这题的OG解释看得有点晕~~~为什么“两个理论的共同点: Astronomers have hypothesized that a meteor stream should broaden with time 和In the model... The researcher found, as expected,that the computer-model stream broadened with time. 都是指随着时间增长, stream越来越宽. 所以老的stream比小的宽大, 从而导致所产生的shower老的比小的时间长. (这个shower是地球穿越这个stream而引起的).”

我的问题是：此题应该是越新的stream比老的宽大阿~~因为它是broaden with time 的ma~~

不知道LZ得问题出在哪里诶。
由于a meteor stream broaden with time，所以an older meteor stream should be broader than a younger one.
而Whenever the Earth passes through a meteor stream, a meteor shower occurs.
也就是说meteor shower的历时是取决于meteor stream的宽度，越宽，历时越长。
又知道老的比新的宽，所以穿越老的要比穿越新的历时长。由此推到D。

关于这篇文章和这道题目，有一个困惑：

通读第一段，发现后面有一个However,自然让读者感到是和前面的内容转折，但读下来却根本不是如此，此处的这个however误导性及其强烈！！以至于注重用关键词看文章结构的同学很容易做错61题：

however前述内容是电脑试验证实了流星群的扩张行为，照理however后面所引出的是传统观点应该与上述“扩张”结果相反，但事实上however后面的内容根本与前文不在相关，而是从此处开始（第一段的最后部分）引出了一个关于流星群的新话题，即，同一轨道上流星群颗粒的分布问题，老观点认为集中，电脑试验认为分散；用来引出老观点的however根本不是与前面的内容转折，而是与后面的内容转折！从常识上、逻辑上看，however放在这里都是不妥当的！

A meteor stream (meteor stream: 流星群) is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on (gain on: v.逼近, 超过, 侵蚀) or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles’ individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation (computer simulation: 计算机模拟) of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower (meteor shower: n.[天]流星雨) occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled “pipe” and one as it exited. There is no reason why the Earth should always pass through the stream’s exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 show just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.

楼上，however的确表示转折，但是不一定是前后内容上的严格对比转折。主要是表示作者行文态度和论述上的转折。文中，however前面谈的是实验和传统在扩张行为方面的说法是一致的，however后面就讲，在中间厚两边薄还是两边厚中间薄的问题上产生了分歧。

这的确是一个很公正的对比，前面讲实验和传统在某些方面一致，后面讲，但是实验和传统在某些方面又不一致。

看到however会产生一个预测，后面和前文内容要不同，有转折了，但是这个不同和转折是多种角度的。