第84题目仍然不是很明白

Passage 14

A meteor stream 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 differeing velocities they slowly gain on or fall behind the disintegrating(碎裂瓦解) comet until a shroud (覆盖)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 experimetn 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 of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected,

that the computer-model stream broadened with time. (上面的hypothesis就是传统理论)Coventional theories, however, predicted that the distribution of particles would be increaingly dense toward the center of a meteor stream. Surpringly, 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 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(86题)? 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.

84：

84. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s orginla orbit?

(A) They are ejected by the comet at differing velocities.

(B) Their orbits are uncontrolled（错误，应该是被万有引力控制） by planetary gravitational fields.

(C) They become part of the meteor stream at different times.

(D) Their velocity slows over time.

(E) Their ejection velocity is slower than that of the comet.

This question asks for the reason given in the passage for a characteristic feature of meteor

streams. According to lines 1-7, the dust particles in a meteor stream eventually surround a

comet’s original orbit because of the different velocities at which they are ejected, as stated in

choice A, the best answer.

Choice B is directly contradicted by information in the passage (lines 8-10). The other answer

choices re incorrect because the passage does not say that the dust particles become part of the

meteor stream at different times, or that their velocity slows over time, or that their ejection

velocity is slower than that of the comet.

虽然定位在line1-7，可是看不出，particle绕那个comet旋转，是由于速度不同造成的啊

请牛人指点

我真没看明白

These particles follow the same orbit as the parent comet, but due to their differeing velocities they slowly gain on or fall behind the disintegrating(碎裂瓦解) comet until a shroud (覆盖)of dust surrounds the entire cometary orbit.

我觉得您点出的这句话应该这么理解吧

由于它们不同的速度，他们渐渐的增加或者减缓速度这样使自身和comet能保持一致，直到一个shroud of dust绕轨道。。。

不同速度是他们gain on或者fall behind的原因，但是不是他们一起绕轨道同步旋转的原因啊

thanks !!!

我的理解是这样的，这些particles由于他们的速度不同而有些在comet前，有些再后，直到最后surrounds the entire cometary orbit。正因为他们有些在comet前面，有些在comet后面，所以会慢慢的包围comet,又因为particles的速度不同，所以才会有些在前有些在后。这个原因要推断。但是这仅仅是从中文上考虑，在“These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary’s orbit.”中，they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary’s orbit.”都是due to differenting velocities.

一家之言，请nn指正

until表示一个过程进行的结果

因为due to their differeing velocities ,发生gain on or fall behind the disintegrating(碎裂瓦解) comet，结果a shroud (覆盖)of dust surrounds the entire cometary orbit

结果和发生过程的原因是一个，即differeing velocities.

These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary’s orbit.”中，they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary’s orbit

对于这句话的逻辑关系,我也是很不明白,尤其是这里关系到Q84的回答,感觉很含混,请NN 解释一下!