The passage first talks about astronomers' assumptions regarding the earth's and
moon's radii and core mass. The next two paragraphs detail the two methods
astronomers employed to analyze their assumptions by using data collected by
Lunar Prospector. The last paragraph discusses the implications of this data.
(A) This choice founders over the use of the singular word "method" and the word
"proved." There were two methods, and "proved" is too extreme.
(B) This choice uses the word "changed," which is factually wrong because the
passage says that it confirmed an assumption.
(C) This choice fails because of the use of the singular "method," and because
"planets" is too general for a passage only concerning the Earth and its moon.
(D) CORRECT. It is acceptable to equate "implications" and "deductions," as well as
"hypothesis" and "assumption."
(E) This choice ignores the entire passage except for the last paragraph, and thus by
definition can not be the passage's sum.
The information to answer this question must come from the second or third
paragraph. As it turns out, the choices all relate to the second one. The second
sentence of that paragraph reads "measured minute variations in radio signals from
Lunar Prospector as the craft moved towards or away from the Earth."
(A) Changes in the craft's velocity were measured while the craft orbited the moon,
not as A states as the craft "returned to Earth."
(B) Although measurements of the Lunar Prospector 's velocity allowed scientists to
create a "gravity map," the scientists did not measure directly the gravitational pull on
(C) This choice is incorrect because the passage does not discuss changes in the
(D) CORRECT. The phrase "changed position relative to the earth" is a fair
equivalent of "moved towards or away from the Earth."
(E) This choice is incorrect because the passage does not discuss changes in the
moon's gravitational pull over time.
This question asks why the author included this detail. The "gravity map" was a step
in the determination of the size of the moon's core. We must find a choice that
(A) This choice is a distortion—the method was not used in this way.
(B) This choice not only comes from the third paragraph but also reverses the
relationship--the magnetic field work confirmed the map.
(C) CORRECT. The author put in the detail to show a step in the investigation of the
core ("composition") of the moon ("orbiting body").
(D) This choice contains the false word "earth"; in fact, the "moon" is the sole focus
of the investigation of gravity's effects.
(E) This choice incorrectly states that an older theory was discarded; in fact the old
assumption was confirmed.
Because the question is open-ended, the best approach is to evaluate the choices.
(A) CORRECT. The information contained in A can be proven from the information in
the passage. The ratios that it discusses can be found in the first paragraph: the
earth's core contributes 55% of the earth's radius and 32% of its mass, compared to
the moon's core contributing 20% of the moon's radius and 2% of its mass. Like
many correct answers to inferences, the inference is very small.
(B) This choice reverses the relationship suggested in the passage--that the moon
might have broken away from the earth.
(C) This choice does not have to be true both because said proof is not certain and
because it is even less clear that the gravity map could be used for that purpose.
(D) This choice is a typical GMAT flight of fancy that sometimes is given as a wrong
choice; as dinosaurs are not mentioned at all, this answer is impossible.
(E) This choice does not have to follow from the information provided. The passage
does not give any information about the percentage of iron in the earth's core nor
does it compare that aspect of the two cores.
KUDOS is the good manner to help the entire community.