The takeaway here is that a lot of idioms can go either way. Because of this you should always solve questions without idioms if possible, and only work on the idioms as a last resort..

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Tim Sanders
Manhattan GMAT Instructor

Hi, can you please help me understand how the other four choices are run-ons or fragments as im unable to identify these issues in the four wrong options.
thanks.

i've yellowed out modifiers to make the below discussion easier.

(a)
Prospecting for gold during the California gold rush was a relatively easy task, because of erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach for anybody with a pan or shovel.

this is "because OF + CLAUSE".
prep + CLAUSE is not a valid sentence structure.

(b)
Prospecting for gold during the California gold rush was a relatively easy task, because of erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of anybody with a pan or shovel.

there's nothing parallel to the boldface construction; "and" requires that there be some parallel construction earlier in the sentence.

(c)
Prospecting for gold during the California gold rush was a relatively easy task, owing to erosion, prehistoric glacier movement, and volcanic activity that had thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of anybody with a pan or shovel.

same problem as in (b).

also, "owing to" is sketchy and informal -- i wouldn't use that in a formal sentence, unless i were actually writing about someone literally owing something (like money) to someone else.

(d)
Prospecting for gold during the California gold rush was a relatively easy task, since erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, putting gold literally within reach for anybody with a pan or shovel.

"since" is a subordinating conjunction, so the words after “since” should constitute a sentence by themselves.
in this example, those words are NOT a complete clause; they're just a noun (X, Y, and Z), followed by two modifiers (the "that" modifier and the "comma + ing" modifier).

Ron, Thanks very much for the wonderfully detailed post.

he's good at that.. :)

_________________
Tim Sanders
Manhattan GMAT Instructor

Hi Ron,
I agree with you that all the other 4 answer choices have 'major' grammatically errors, and hence cannot be the correct answer choices. However in the correct choice E, dont you think the 'logical parallel structure' has not been followed?

In this option, Erosion and Glacier movement are parallel to 'riverbeds'. Dont you think the correct noun to be paralled is 'volcanic activity'? Also it is in passive voice - riverbeds thrust to the surface by volcanic activity!

Can you please comment on this? Thanks

Well, I find the idiom "within reach for" less congenial than does Jonathon, but it's really an empirical question, or a couple of empirical questions:

1) Does the GMAT ever count "within reach for" as correct? Not to my knowledge, but the issue is so rare that you can't draw any conclusions. I dunno.

2) Does the GMAT ever require that you recognize "within reach for" as wrong in order to eliminate an otherwise incorrect answer? Not to my knowledge, but the issue is so rare that you can't draw any conclusions. Still I doubt it, so I sort of agree with Jonathon after all.

As to your immediate question, no. Consider a sentence such as "Home ownership is with reach." Great, but for whom? "Home ownership is within reach for families with two wage-earners and good credit." This means the same as "Home ownership is within reach of families with two wage-earners and good credit." I think that the structures are different, that "for families..." modifies the entire preceding clause, while "of families..." modifies the noun "reach." But that's too arcane a concern.

Dear Instructor,
Is there an easier rule that can be learnt from this question re: "because of" use. I am still strugling seeing why A and B are wrong.
thanks

choice (a) has "because of" followed by a clause, not just by a noun (or collection of nouns). you can't do that; prepositions must be followed by nouns, and can't be followed by clauses.

choice (b) contains "...and putting". and signals parallelism, but there's nothing parallel to "putting".

Hi Ron,
Thanks for your explanations.

i have a follow-up question from your explantion of A



Does this rule(Prep + Clause is not valid sentence structure) apply in all cases ?

Just to confirm - is this a preposition ? I am confused

Prospecting for gold during the California gold rush was a relatively easy task,

yes.



whoa, no. the preposition in this case is “of”.

it seems that you ought to go look up the definition of a preposition -- the best way for you to do this is to use a search engine; there will no doubt be hundreds, if not thousands, of good websites carrying definitions of basic grammatical terms such as this one.

Thanks Ron - Just one doubt here so is it "BECAUSE + PREP" cannot be followed by Clause or any PREP cannot be followed by a clause. Just a little bit confused. Can you please enlighten us with some examples please, will help a lot..!

prepositions can't be followed by clauses. they must be followed by a noun (or noun + modifier).

since this is completely general, just use google (search for "preposition usage", or "prepositional phrase examples", or whatever else) to find examples.