Reading Comprehension Home Exercise – 01, PASSAGE D

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; butt 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 5000 –ear- 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, predicated that his distribution of particles would be increasingly dense toward the centre 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 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 centre, 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.

17.       The primary focus of the passage is on which of the following?

A.      Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon

B.      Describing a new theoretical model and noting that it explains the nature of observations made of  particular natural phenomenon

C.      Evaluating the results of a particular scientific experiment and suggesting further areas for research

D.      Explaining how two different natural phenomena are related and demonstrating a way to measure them.

18.        According to the passage, which of the following is an accurate statement concerning meteor streams?

A.      Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.

B.      Meteor streams grow as dust particles are attracted by the gravitations fields of comets.

C.      Meteor streams are composed of dust particles derived from comets.

D.      Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.

Answers and Explanations 

 17.       B     To answer a question about the primary focus of a passage, look at the passage as a whole. The first paragraph describes the new theoretical model. The second paragraph discusses the data relevant to actual observation, and the third paragraph shows that actual observations were consistent with the theoretical model. 

  18.       C     The phrase according to the passage indicates that the answer is explicitly stated in the passage; however, it may be stated in slightly different language. The passage begins with a definition of a meteor stream, which is composed of dust particles that have been ejected from a parent comet at a variety of velocities.