Here's the
official explanation provided by the GMAC for this question:
There is no doubt that this sentence is supposed to communicate certain facts about an asteroid: the asteroid is traveling at 46,000 miles an hour, it is orbiting the Sun, it takes a year to complete the orbit, the orbit is elliptical, and the asteroid regularly returns toward Earth. When these facts are all communicated in a single concise sentence, the structure needs to be grammatically correct and to indicate the relationships precisely and logically.
Option A: There is little doubt about the intended meaning of
an elliptical path that orbits the Sun. But this is an imprecise and nonstandard way of expressing the idea, and this wording is vulnerable to a joking or uncooperative reading whereby the path, rather than the asteroid, is claimed to be traveling on an orbit around the sun. One might guess that
it refers to the asteroid, but it could, for example, refer—nonsensically—to the Sun
.Option B: Correct. This is grammatically correct and clearly expresses the fact that the asteroid orbits the Sun and that the elliptical path regularly brings the asteroid back toward Earth.
Option C: This could be read as saying that the asteroid regularly brings the asteroid on an elliptical path back toward Earth. The wording also oddly suggests that the asteroid may not be on the elliptical path except when it is on its way back toward Earth. The wording
once a year orbits the Sun is awkward;
a year could be uncharitably taken as the subject of
orbits. The pronoun
it can be read as referring to
the Sun, but this reading is not likely to be what is intended.
Option D: With this wording, the part of the sentence following
Scientists calculated that is ungrammatical; it has three participles (the verb forms ending in
-ing) but no main verb.
Option E: This is ungrammatical. If
that is intended as a relative pronoun (equivalent to
which), it has no clear referent and the structure of the sentence does not make sense. It is plausible to think that
that is intended as a demonstrative pronoun, referring either to the path or to the asteroid’s orbiting the Sun on an elliptical path. If so, there should be a comma after
year to clarify the intended grammatical structure.
The correct answer is B.
Please note that I'm not the author of this explanation. I'm just posting it here since I believe it can help the community.