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. That means it will support the conclusion without bringing in anything new.

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

the new screening test can prompt dangerous operations that actually are not medically necessary.

Medical researcher: [BACKGROUND]. But [SUPPORT]. Yet [SUPPORT]. Thus, [CONCLUSION].

There’s new wording in the conclusion that signals the author changed the subject. Did you recognize it? They brought in “medically necessary”, which isn’t explained or even mentioned anywhere else in the passage. The right answer will connect that wording to the key piece of support that “polyps turn out not to be malignant”.

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

(A) …is ethically justified only for…

The passage doesn’t say anything about whether anything is “ethically justified”. That’s not the same thing as “medically necessary”.

(B) Surgical removal of nonmalignant polyps…is not always medically necessary.

Sounds pretty close to the conclusion, doesn’t it? This is making the exact connection you want to see between the new wording in the conclusion and the rest of the argument, without bringing in anything new. If the author’s conclusion is right, this would have to be true too.

(C) …it either should not be used or its use should be modified.

It could be reasonable to draw this conclusion based on the passage, but that’s not what you’re being asked for. This doesn’t have to be true to make the conclusion the work. The conclusion doesn’t say anything about whether the test should be used. You can’t assume that just because the author says the operations aren’t “medically necessary”.

(D) …should be surgically removed if it is malignant.

The argument doesn’t say anything about whether a polyp should or should not be removed. That’s not the same as saying the operations “are not medically necessary”. That’s bringing in something new, and so it doesn’t have to be true to make the conclusion work.

(E) …medically useful only when…

One more time, that’s not the same thing as “medically necessary”, which is the wording the passage uses. There could be plenty of other uses for the screening test that aren’t talked about here. No way this has to be true based on the conclusion.

(B) is the correct answer.