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

Only the right answer will be support that must be true if the conclusion is true, or more simply you could say only the right answer will be support that doesn’t bring in anything new.

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

there is actually no reason to believe that the hypothesis is correct

Professor: [BACKGROUND]. [BACKGROUND]. But [CONCLUSION], since [SUPPORT].

This is another one that changes the subject by bringing in new wording at the end. The author doesn’t actually give any evidence against the “light-absorbing medium” idea, they just start talking about “the general theory of relativity” instead. How do we know those two aren’t the same thing? The author doesn’t explain any connection, so that’s what the right answer will call out.

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

(A) …would not be adequately explained by the existence of an invisible light-absorbing medium…

The author didn’t say it this strongly. Their argument isn’t that the “light-absorbing medium” thing couldn’t possibly work, just that there’s “no reason to believe” it’s right. Those aren’t the same. As long as the low visibility thing is “completely explained” be relativity, the conclusion could still work, even if this “medium” could also “adequately explain” it.

(B) …correct only if it adequately explains…

Careful, the argument isn’t actually about whether the hypothesis is “correct”. It’s about whether there’s “reason to believe” it’s correct. Those aren’t the same. There could still be “no reason to believe” even if there are other ways for the hypothesis to be correct.

(C) A hypothesis is likely to be correct if…

The argument doesn’t rely on any rules about what makes a hypothesis “likely to be correct”. It’s only about the “reason to believe” a hypothesis is correct. This answer doesn’t connect to the wording of the conclusion well at all.

(D) Most scientists who posit…

The conclusion is only about the hypothesis itself. Nothing has to be true about “most scientists” for that conclusion to be valid.

(E) …relativity does not depend upon the hypothesis…

Boom. Finally an answer that connects the two different subjects in the passage. If the low visibility thing is “completely explained” by relativity, and that’s why we can dismiss the “light-absorbing” hypothesis, then we’re definitely saying relativity doesn’t include the hypothesis. But for all we know, relativity is the light-absorbing hypothesis. The author is definitely assuming one “does not depend upon” the other.

(E) is the correct answer.