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Polio - OG explanation confusion

Expert replies

by GMATGuruNY » Sun Aug 01, 2010 3:47 pm
uwhusky wrote:This is what the answer explanation said:

"This sentence makes two main claims about a single subject, polio (that it continues elsewhere, and that it can be brought back into the United States). The claim that polio has been eradicated in the United States is a condition of the other two claims and is best expressed in a subordinate clause."

Then it goes into explanation of each answer.

So my confusion is if "could" and "can" is used as different meaning as oppose to different tense, why is it the explanation use "can" when the context remains the same and the answer says "could".

But thank you very much for the added example of the difference in tense, I think I sort of understand the concept a bit better now. So "could" and "can" are different in terms of meaning, but "could" can be used as past tense for "can" under certain context, and same with vice versa?
I wouldn't worry about why the explanation uses can when can is used only in an incorrect answer. Our goal is to find the most efficient way to eliminate the four incorrect answers; this is not the goal of the explanation above.

Observing the errors that I pointed out in my initial response is the most efficient way to eliminate A, B, C and D.
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