PT18.S2.Q06 - a study was designed to establish what effect

Samcandoit!

http://7sage.com/lsat_explanations/lsat-18-section-2-question-06/
Could someone please explain this question for me. I am little confused by B, C, D.

Matt1234567

Tricky question, and a very subtle assumption that will lead you right into the correct answer choice.

Conclusion: Oil rigs have no adverse effect on sea-bottom animals.
Premise: The study compared sea-bottom communities near rigs with those located in control sites several miles away from any rig and found no significant differences.

So there's a comparative study happening to research the effect of oil rigs on sea-bottom animals. Two areas are studied, one near a rig, and one several miles away from any oil rig. The argument makes the assumption that sea-bottom communities near oil rigs should be affected, and it also assumes that sea-bottom animals away from any oil rig will not be affected because of the distance of several miles. It bases its observation on the similarities between the two sites on the fact that there is "no significant difference" and then concludes that there are no adverse effects.

For us to conclude that, we need to know that oil cannot spread several miles away, or in other word, the sea-bottom animals that are several miles away are not affected by oil rigs. If it were the case that oil could spread several miles to these sea-bottom animals, then maybe that's why there's no significant differences between the two fishes? Therefore, it would weaken our conclusion that oil-rigs have no adverse effects on sea-bottom animals. Answer (B) gets to the heart of this assumption by saying that water currents carry oil discharges from oil rigs 'considerable distances" before it settles on the ocean floor.

Both C and D are both kind of useless to the conclusion. One talks about sewage and industrial contamination of ocean, and how it reduces diversity, and the other says that not all of the oil reaches the bottom of the ocean. Okay, but is there an adverse effect on sea-bottom animals from oil rigs or no?

Samcandoit!

@Matt1234567 , thank you so much. Your answer is very comprehensive and helpful.