responses point by point:
phuonglink Wrote:(A): "which" followed by comma is expected to modify "an acre", "in the Louisiana purchase, U.s" is wierd in meaning
i think you have the right idea in your discussion of "which", but, just to clarify -- that "which" is
trying to refer to the entire idea of the preceding clause, but grammatical rules will allow it to apply to, at the very most, "four cents an acre".
regarding the initial modifier ("in the louisiana purchase"), no, that's incorrect -- generally, when a sentence starts with a prepositional phrase in front of a comma, that prepositional phrase modifies the meaning of the entire clause that follows. so this modifier is fine.
(B): acquire should plus something
i'm not really sure what this means.
if you mean that the word "acquire" should have an object, note that it does -- "828,000 square miles", which is admittedly placed in a strange location (after another modifier), but is there.
here are a couple of more serious problems that i see with that answer choice:
* the repeated pronoun "it" is inappropriate if you have two actions, with the same subject, connected by "and". this is a rather arbitrary convention -- probably aimed at making sentences more readable while reducing redundancy -- but it's pretty firm: for example, "james drank a glass of water and took a nap" is considered a proper parallel structure while "james drink a glass of water and
he took a nap" is not. in general, you don't use a second subject in such parallel structures, unless it's a
different subject.
* the parallelism exists between "it brought..." and "the united states acquired...". this parallelism is inappropriate, suggesting that
both of these events occurred at a rate of four cents per acre (nonsense for "it brought..."). moreover, the elements that
should be parallel (the forms of "double" and "bring") aren't parallel; this kind of "mistake by omission" is also a mistake.
(D): is bad in structure with xxx,xxxx,xxx,xxxx,xxxxx
ya -- more precisely, this choice has an -ING modifier modifying another -ING modifier. i don't think that's a legitimate structure; at the very least, i have certainly never seen it in any halfway legitimate official sentence.
(E): we have pronoun shift: "it" and "its" modify 2 different things which is not allowed in writing (Ron said)
Please correct me if i'm wrong.
hmm yeah -- that's an issue here, but note that the "it" and "its" are in different clauses. moreover, note that the noun "country's", which intervenes between those two pronouns, conveniently serves as a referent for the pronoun "its".
this is one of those sentences in which a native speaker's first reaction would be something along the lines of, "huh? i can't tell at first glance what that pronoun stands for". ... but let me try to come up with something specific:
the intended referent of the pronoun is used:
* prior to the pronoun
-- AND --
* in a modifier between commas
if a referent ever satisfies both of these criteria, it is very unlikely that it's a legitimate referent for a pronoun.