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

Only the right answer will accurately describe what kind of support, conclusion, or background the claim is.

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

Our mastery of Latin and Ancient Greek is at best imperfect.

Classicist: [CONCLUSION]. [BACKGROUND]; but [SUPPORT].

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

(A) It is the main conclusion…

No it isn’t, it’s support for the conclusion in the first sentence.

(B) It points up by example a contrast from which the conclusion is drawn.

Weird wording, but that’s never a good reason to eliminate an answer. Is it an “example”? Hell yes, it’s one instance meant to support a more general overall point. Is it meant to highlight a “contrast”? For sure, the contrast is between the students who “immerse themselves” and the reality that “you cannot travel back in time”. And support is exactly the thing “from which the conclusion is drawn”.

(C) …no logical relation to the argument’s conclusion.

That would map to background info, not support.

(D) It is a premise that guarantees…

Whoa, too strong. The claim backs up the conclusion but definitely doesn’t “guarantee” it.

(E) It is an ancillary conclusion…

Nope, there’s no support given for it. It’s just a fact, so it’s not a conclusion.

(B) is the correct answer.