B it is.
B. You got it? The data given may or may not be respresentative. i.e the decrease in the extinction between 1950 and 2000 is because of what reason? This is what you want to evaluate.
Could you please restate your reasoning?
Zoologist warns of increased extinction. But past data says that extinction is decreasing.
B. Has any special effort been made to save North American insect species?
YES or NO
Evaluation of argument:
If answer is YES then we can say that the zoologists are right and the drop in extinction is due to these efforts.
If the answer is NO then we can say that zoologists are wrong and extinction will not increase because past trends are not like that.
So choice B's answer empowers you to evaluate the argument. You can not evaluate the argument by answering any of other choices.
Hope this helps.
SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008