Sentence Correction

hey -- this is one of the worst official problems i've seen, but, at the same time, it is an official problem, so we've got to learn from it.

you can strike the last two choices because they use "and" where they shouldn't -- a common mistake in spoken english. ironically, if you're a non-native speaker, you are probably a lot less likely to be fooled by these choices; the primary victims of incorrectly used "and" are native speakers, since "and" is grossly overused in just about every imaginable context of spoken english.
you should only use "and" when you are talking about two separate actions/things, unless "and" is paired with other words implying a relationship (such as "thereby" or "thus").

e.g.
there was a great deal of traffic today, and i was late to work --> this sentence actually implies that the traffic was NOT the reason why i was late to work; "and" implies that these two facts are separate and independent.
but
there was a great deal of traffic today, and i was thus late to work --> this sentence correctly implies the relationship, by using "thus".

so (d)/(e) are incorrect because they imply that "powering the sun, the stars, and hydrogen bombs" and "merging the nuclei of atoms" are just two separate things that nuclear fusion can do independently of each other. in context, this doesn't make sense; it's pretty clear from context that "merging the nuclei of atoms" is the way in which nuclear fusion powers these things.

--

also:
you have to treat "X AND Y" as a SINGLE UNIT.
any modifier that modifies "X AND Y" must modify the whole thing, unless it contains words (such as "former" or "latter") that expressly isolate either X or Y.

so, in choice (a), "as in nuclear reactors" necessarily must modify all of "merging the nuclei of atoms and not splitting them apart".
that doesn't make sense; this modifier is only meant to modify the latter half of this compound. so (a) is incorrect.

--

as for (b):
when you use a "LIKE" modifier, the comparison is automatically made with the SUBJECT & ACTION of the modified clause.
for instance:
jim is friends with tom, like dave.
--> this MUST mean that:
* jim is friends with tom
* dave is also friends with tom
it CANNOT mean that jim is friends with both tom and dave.

applying this principle to choice (b), we arrive at the conclusion that nuclear reactors must do the same thing that nuclear fusion does. that's illogical here, since the entire point of this sentence is to contrast the two.

--

that leaves (c), which is still horrendously ugly, but is still the least ugly of the five.

uwhusky wrote:Hey Ron,

In the case of using "and", let's assume for a second that both verbs are referring back to the force, would it be safe to say that GMAT would write it as "Nuclear fusion is the force that powers..." and "that merges..."

not the point -- this isn't a grammar issue. there's nothing wrong with the existing grammar; the issue is that "and" doesn't make sense.
this is not a problem of mechanics; it's impossible to detect a problem here by thinking about mechanical/grammatical issues.

the meaning of the sentence is that "merging the nuclei" is the way in which nuclear fusion powers those things. they are not two separate actions (see my examples above), so any construction that just connects them with "and" is going to be incorrect, unless you use "thereby" or some other word that correctly expresses the relationship.

--

same thing:
if i go to work today by driving on the freeway, it's incorrect to say "i'm going to take the freeway AND go to work."
this sentence is not ungrammatical -- it just doesn't make sense. the implied meaning is that i'm going to "take the freeway" (going to i-don't-know-where) and then, separately. i'm going to go to work.

uwhusky wrote:

lunarpower wrote:also:
you have to treat "X AND Y" as a SINGLE UNIT.
any modifier that modifies "X AND Y" must modify the whole thing, unless it contains words (such as "former" or "latter") that expressly isolate either X or Y.

so, in choice (a), "as in nuclear reactors" necessarily must modify all of "merging the nuclei of atoms and not splitting them apart".
that doesn't make sense; this modifier is only meant to modify the latter half of this compound. so (a) is incorrect.

Ron,

Can you please elaborate on the point above, how do you determine whether the modifier is modifying all as oppose to partial?

do you mean grammatically, or do you mean in terms of context?

grammatically, it's simple -- you should basically think of "x AND y" as a single word. so, as required by grammar, any modifier that tags "x AND y" must tag all of it.

the crux of the issue, then, is determining whether that's what you actually mean.

in this sentence, that's not what we actually mean, since nuclear reactors don't do both of these things.
there's no mechanical way to figure this out; you have to figure out meaning by thinking about meaning.

--

simpler analogy for the above issue with "and":

let's say that BOTH tom and dave went to brazil last month.
...then if i write
i talked with tom and dave, who went to brazil last month
... then that's correct, since the modifier necessarily tags "tom and dave".

BUT
if only dave went to brazil, then
i talked with tom and dave, who went to brazil last month
is INCORRECT, because the modifier must still modify both tom and dave. if the intention is for the modifier to tag only dave, then you can't do this.

two ways to fix:
1) use "the latter"
i talked with tom and dave, the latter of whom went to brazil last month
(this is somewhat cumbersome, but at least it's correct)
or
2) split the construction
i talked with dave, who went to brazil last month, and with tom.
i talked with dave, who went to brazil last month, and tom.
both correct.