Question

According to the National Agricultural Aviation Society (NAAS), without the use of crop protection products to control insects, weeds, and diseases, crop yields per acre will drop by more than 50 percent. The first aerial application of insecticide occurred in 1921, and it was a huge success. By contrast, in today's economy all aircraft that are classified as aerial applicators do more than just apply insecticide; today, they also spread seeds and apply fertilizer.

From the information given above, it CANNOT be validly concluded that:

• A. According to the NAAS, if crop yields per acre never drop by more than 50 percent, then crop protection products have been used to control insects, weeds, and diseases.
• B. In today's economy, any aircraft that cannot be used to apply fertilizer cannot be classified as an aerial applicator.
• C. In today's economy, if an aerial applicator is used, then it will be able to spread seed and apply fertilizer.
• D. According to the NAAS, if crop yields per acre drop by more than 50 percent, then crop protection products have not been used to control insects, weeds, and diseases.

Hint:

Check whether each option swaps and negates both sides of the passage's rule, or whether it just reverses the rule without negating it.

Answer 1

The Correct Option is D

Mark using protection as $P$ and a yield drop past 50 percent as $Y$. The passage gives one rule: not $P$ leads to $Y$. Check each option against this rule.

1. Option A: This reads as not $Y$ leads to $P$. Swapping both sides and negating them on a true rule always gives another true rule, so option A holds and is not the answer.
2. Option B: The passage's second line says every aerial applicator today can also spread seed and apply fertilizer. Let $F$ mean able to apply fertilizer. Option B reads as not $F$ leads to not an aerial applicator, the same swap and negate move on a true statement, so it holds.
3. Option C: This just restates the second sentence directly (an aerial applicator can spread seed and apply fertilizer), so it clearly holds.
4. Option D: This reads as $Y$ leads to not $P$, which is a plain reversal of the rule (not $P$ leads to $Y$), not a swap and negate. A plain reversal of a true rule need not be true. A bad season, a new pest, or a drought could push the yield loss past 50 percent even when protection products were in use.

Only option D fails this check, so it is the statement that cannot be validly concluded.

Let's summarize:

• Swapping and negating both sides of a true rule (the contrapositive) always stays valid.
• Simply reversing a true rule (the converse) is not guaranteed to hold.
• Option D makes this reversal error, which is why it is correct.

Final answer: $\boxed{\text{Option D}}$