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

Only the right answer will explain the study, basically supporting the conclusion that the results aren’t “surprising” after all.

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

There is no conclusion in the passage.

[BACKGROUND]. [BACKGROUND].

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

(A) …the amount of rainwater that falls into Crystal Bay is negligible.

Then it wouldn’t have much effect, so that wouldn’t explain why pollution is at the “highest levels.”

(B) …falls on pesticide-treated fields before…

So it picks up pollution along the way. That would explain it for sure.

(C) …evaporated from oceans around the world.

That is truly fascinating, but this isn’t about where the rain falls, which is the only part the passage talked about.

(D) The single leading cause of pollution…

…is really specific information that brings in new wording the passage doesn’t use, and doesn’t tell us about the effect of the “heavy rainfall”.

(E) …that is extremely similar to that of Crystal Bay.

That might rule out causes that are specific to Crystal Bay, but it doesn’t do anything to explain what is happening.

(B) is the correct answer.