Q9 - The local agricultural official gave

[WaltGrace1983]

This was a very tricky question because of the double-negatives (at least to me).

During 3 years of NEW pesticide, less pears were lost than during the preceding 3 years of OLD pesticide
-->
NEW pesticide = more effective than OLD pesticide

This is a correlation/causation issue. Just because two things correlation (new pesticide and dwindling loss) does not mean that one causes the other. Maybe unseasonably dry weather killed all the pests and the pesticide had nothing to do with it?

However, we want to strengthen the idea that the new pesticide was more effective than the old pesticide by saying that a particular group of trees did NOT show a reduction in losses.

In other words, NO REDUCTION in LOSSES means having an equal or greater amount of LOSS.

This goes starkly against the "typical" strengthen question and so it is very important to be very clear about the language. We want an answer choice that shows the OLD pesticide having "no reduction in losses."

(A), (B), and (E) all refer to the NEW pesticide. If the NEW pesticide had "no reduction in losses," then this would most likely mean that the NEW pesticide is actually NOT as effective as the OLD pesticide. This would weaken the argument.

(D) doesn't help nor hurt us because it doesn't address either pesticide.

The only logical answer, therefore, is (C). If the OLD pesticide had no reduction in losses while the NEW pesticide showed a great reduction in losses (we know this from the premises), this gives us more reason to believe that it was the NEW pesticide that caused the reduction in losses.

Hope that helps.