How will the right answer fit in terms of support and conclusion?

Only the right answer will match the conclusion.

Highlight the main conclusion in the passage, if there is one:

This would, however, be a temporary solution at best

Essayist: [BACKGROUND]. [BACKGROUND]. [CONCLUSION]: [SUPPORT].

You can smell the conclusion coming if you recognize background info that sounds like ‘Some people say…’ Those outside arguments usually set up that the author is gonna disagree, and that disagreement will be their conclusion. So once you read, “Some people have claimed…”, there’s no doubt what the conclusion will be.

Map the wording of the answers to the wording of the passage:

(A) If Earth’s population continues to grow…

This is the background info in the first sentence. There’s no support given for this, so you know it can’t be a conclusion.

(B) …the problem of overpopulation of Earth will probably persist.

The author never actually said this, so no way it’s their conclusion. Make sure you’re clear that saying the problem will continue isn’t the same as saying an idea for a solution would be “temporary”.

(C) …and if at some point half of the population…

This maps pretty closely to the support that follows the conclusion, although it actually misquotes the author here by leaving out “the year 2500”.

(D) …will probably continue to grow geometrically even if…

This is misquoting the author. There’s nothing that means “even if” in there. It’s fair to say the author is implying this, but that’s definitely not the same as drawing a conclusion.

(E) …would, at best, be a temporary solution…

This is a pretty perfect match for the author’s conclusion.

(E) is the correct answer.