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 differing velocities they slowly gain on 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 position 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. 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 occurs. Moving at
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.
PREP2012-Pack1-RC-002-02 VRC07544-02 Hard
It can be inferred from the passage that which of the following would most probably be
observed during the Earth's passage through a meteor stream if the conventional theories
mentioned in the highlighted text were correct?
A. Meteor activity would gradually increase to a single, intense peak, and then gradually
decline.
B. Meteor activity would be steady throughout the period of the meteor shower.
C. Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
D. Random bursts of very high meteor activity would be interspersed with periods of very
activity.
E. In years in which the Earth passed through only the outer areas of a meteor stream,
meteor activity would be absent.
Inference
An inference is drawn from stated information. Begin by looking at the information about
conventional theories in the sentence containing the highlighted text. Conventional theories
held that the distribution of particles would be increasingly dense toward the center of the
meteor stream. If the conventional theories were true, it could be inferred that there would
be one intense period of activity as the Earth passed through the dense center of the meteor
stream. The computer model showed instead that meteor stream resembled a thick-walled,
hollow pipe. The next-to-last sentence of the second paragraph explains that, according to
the computer model's prediction, Earth would experience two periods of meteor activity as it
passed through the meteor stream, one as it entered the “pipe" and one as it exited.
Observation of the Geminid meteor shower shows just such a bifurcation.
A. Correct. Since the conventional theories predicted an increasingly dense center, Earth
would experience a gradual increase of meteor activity, an intense peak at dense
center, then a gradual decrease.
第二题不懂 为什么a选项 另外 文章的逻辑结构不懂作者: DeliciaAn 时间: 2015-3-24 11:55
It can be inferred from the passage that which of the following would most probably be observed during the Earth’s passage through a meteor stream if the conventional theories mentioned in line 18 were correct?
(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.
第2段： “Twobrief periods of peak meteor activity during the shower would be observed, oneas the Earth entered the thick-walled “pipe” and one as it exited. 这句话写的是computer-model G stream.就是说两个到峰值的时间是Earth 进入了个中空壁厚的结构中，就是在开始的时候达到peak,在exist的时候又达到了peak.”
infer题用于推理。看到第一段“Conventional theories, however, predictedthat the distribution of particles would beincreasingly dense toward the center of a meteor stream. ”
综上，conventional theories是跟新的G stream代表的理论是相反的，就是不是两边峰值中间不峰值，而是中间峰值两边不峰值。
再看a选项：(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline. 先增加，达到了顶峰，然后又下降了。
符合。
所以选择A
以上为个人对这道题的一点浅见，还请各位牛牛批评指正。
作者: 典座 时间: 2020-9-22 10:26
DeliciaAn 发表于 2015-3-24 11:55
It can be inferred from the passage that which of the following would most probably be observed duri ...