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

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

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

the sole reason that sexual reproduction has become the rule among both animals and plants is that natural selection has favored some entire species over others.

Biologist: [BACKGROUND]. However, [SUPPORT]. It follows that [CONCLUSION].

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

(A) It is a claim offered in support…

Indeed it is. They call this ⭐⭐⭐, but “It follows that” should make the structure pretty clear. You could definitely just pick this and move on.

(B) …to raise a question…

Where do you see a question being raised? Yah, me neither.

(C) …to call into question.

The argument doesn’t call anything into question. There’s no wording to match that description.

(D) …for which the argument seeks an explanation.

Conclusions are the part “for which the argument seeks an explanation.” This is support. If this wants to be right, you’d see a “because” in there to signal “an explanation” being given.

(E) …the origin of an observed phenomenon.

Be careful, the argument never touches on how something got started in the first place.

(A) is the correct answer.