lunarpower wrote:question #3:

The passage is primarily concerned with

this is a MAIN IDEA question.

if you notice a MAIN IDEA question, your best bet is to:
* COVER the choices (yes, physically ... with your hand or notepad) before looking at them
* PREDICT the answer
* CHECK
otherwise, it's easy to be led astray by tempting, but wrong, answer choices.

if you have trouble doing this -- i.e., if you naturally have a very detail-oriented disposition, and generally have trouble "grasping" main ideas in passages across the board -- then you can always try just eliminating choices containing things that don't appear in the passage.
for instance:

A) analyzing data from a 1994 exploration of lunar surface

the passage doesn't contain any "data" -- just generalizations. ("Data" generally refers to numerical statistics.)
so, auto-wrong.

B) reconciling two opposing theories about the origin of lunar impact basins

the passage contains only one theory -- that of the scientists. ("One would expect..." is NOT a theory.)
so, auto-wrong.

C) presenting a possible explanation of a puzzling finding about lunar impact basins

yep.

D) discussing how impact basins on the Moon's surface are formed

this is in the passage, but it's not the main focus; it's a background fact.

E) examining the claim that the moon's impact basins show negative gravity anomalies

to "examine a claim" is to QUESTION whether it is right or wrong. that doesn't happen here; the FACT that the moon's impact basins show negative gravity anomalies is ... well, a FACT.