请教紫皮Verbal 62

lukeleng

第二段最后一句so the time interval between the two bursts of activity would vary from one year to the next（省略year）．两次高峰期的间隔时间，一年的同下一年的会不一样

第三段第一句Has the predicted twin—peaked activity been observed for the actual yearly Geminid meteor shower?Geminid meteor shower每年出现一次

niswzzhn

A meteor stream is composed of dust particles that have been ejected from a pa rent comet at a variety of velocities．These particles follow the same orbit as the pa rent 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 1000··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．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 a little over 1500，000 miles per day around its orbit，the Ear七h 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 Earl[h 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 1000 years old．

62．It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

(A)  Most meteor streams it encounters are more than 2，000 years old．

(B)  When passing through a meteor stream，it usually passes near to the stream's center．

(C)  It crosses the Geminid meteor stream once every year．

(D)  It usually takes over a day to cross the actual Geminid meteor stream．

(E)  It accounts for most of the gravitational perturbation affecting the Geminid meteor stream．

请问大家这道题目为什么选C啊，看不懂解释，谢谢大家。