Q25 - the populations of certain

[ohthatpatrick]

There IS strong language in the conclusion, so we ARE justified in saying the author makes a strong assumption, but the conclusion is not about what caused the recent amphibian decline.

(C) is about what caused the recent decline.

Our conclusion is actually about "whether it's possible to know something for sure". It's only about whether certainty of a certain idea is possible.

What does the Question Stem tell us?
Necessary Assumption

Break down the Stimulus:
Conclusion: It's impossible to be sure that recent amphib. decline is from pollution. Evidence: Most amphib species vary greatly from year to year.

Any prephrase?
It's tricky to predict what missing idea we need. I would prephrase my normal debating mindset .. "Given that I have to accept that most amphib's vary greatly from year to year, how can I argue that it IS possible to be sure that recent declines are due to pollution?"

Answer choice analysis:
A) When we negate this, it says that the amphibs that recently declined are KNOWN to be amphibs whose population does NOT vary greatly from year to year. Since this renders the author's lone premise as completely irrelevant, it destroys the argument.

B) If natural variations are ALWAYS as large as this recent variation, that would strengthen the argument.

C) If we negate this, it's saying maybe both things caused the decline or maybe some third factor we haven't mentioned caused the decline. None of those ideas hurt the argument. The author's argument is about unclear data. Our author is never saying that pollution is NOT the cause. She is saying that we can't know for sure because we have to worry about natural variation being the cause.

D) This is super extreme. This also has the point of view of someone who thinks that industrial pollution IS the cause. Our author is noncommital.

E) No one in this argument was ever connecting pollution as a cause of extreme weather.

The correct answer is A.

Takeaway/Pattern: One way to cripple an argument, without actually contradicting its conclusion, is simply to remove the premise from consideration. The author's only premise is that "we need to consider that MOST amphibs vary greatly in population from year to year". The correct answer, when negated, is saying "No we don't. The type of amphibs that declined are NOT those type, so that idea has no bearing on them."

#officialexplanation

[ganbayou]

I chose C because of the strong language in the conclusion. why is the answer A?