Don't know if this is good enough since two of the great experts in the forum have already replied.
In the 1960s, surveys of Florida's alligator population indicated that the population was dwindling rapidly. Hunting alligators was banned. By the early 1990s, the alligator population had recovered, and restricted hunting was allowed. Over the course of the 1990s, reports of alligators appearing on golf courses and lawns increased dramatically. Therefore, in spite of whatever alligator hunting went on, the alligator population must have increased significantly over the decade of the 1990s.
Which of the following, if true, most seriously weakens the argument?
Crux of the argument: Surveys in 1960s indicated dwindling alligator problems thus hunting was banned. In early 1990s the alligators populations increased and hunting with restrictions was allowed. But in the 1990s the human-alligator encounters increased as more and alligators were reported appearing on golf courses and lawns. Author concludes that, although alligator hunting was there, the population of alligators kept increased.
Here, author basically theorizes that witnessing alligators in people's lawns and golf courses is sign of increase in alligator population. So, there's a casual relationship between humans and alligators as author sees it. Strengthener would be something that supports author's reasoning. But the argument can be weakened in two ways:
1. Something else caused/led those alligators to go to people's lawns and golf courses. May be they had a gold rush moment and wanted to join exclusive golf clubs
2. Not alligators but people entered the alligators' territories. This has tow sub-cases btw
- Alligators population decreased
- Alligators population remained at same level at it was in early 1990s.
At this point it would look easy to just glance at the right answer but just check other options before looking at the right one.
A. The human population of Florida increased significantly during the 1990s. - CORRECT. This looks neutral to initially, if someone has not figured out yet what is the possible relationship between humans and alligators. From a causality point authors says seeing alligators in people's lawns and golf clubs is a signal that their population has increased i.e. X ----> Y but its the other way round Y ----> X as suggested in this option. A Venn diagram concept may help us here to understand. The common part of the two circles is the golf course and lawns. Either alligators increased that area(strengthener) or the humans increased it(weakener)[Though subconsciously i feel this is the worst example/concept application i have ever thought

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B. The hunting restrictions applied to commercial as well as private hunters. - WRONG. So what if it did, it doesn't impact the conclusion. There's no relationship here neither suggested.
C. The number of sightings of alligators in lakes and swamps increased greatly in Florida during the 1990s. - WRONG. So the expanse of alligators sightings increases. Wow it strengthens the argument which is opposite to what we are looking for.
D. Throughout the 1990s, selling alligator products was more strictly regulated than hunting was. - WRONG. More the products, more the hunting. Here the situation is restricted hunting ---> regulated products. Again strengthens the argument.
E. Most of the sightings of alligators on golf courses and lawns in the 1990s occurred at times at which few people were present on those golf courses and lawns. - WRONG. This is the closest to being a correct answer. But if people are not present on those golf courses and lawns, are the alligators not there. No, this is not the case alligators are still there - either with increased or decreased population. Its a neutral case as far as i see.
A short note: Initially, I fell for the contrast brought by the author to solidify his/her argument. I almost thought that because author in his/her conclusion uses "in spite of whatever alligator hunting went on" to stress upon the hunting part, hunting was without restrictions. Many of us might do so but its not - hunting's still restricted.Also, had even one of the pre-thinking points of
jayarora been there in the five choices, the questions would have been more difficult since it would have fit our point 1 of weakener as above.
IMO Answer A.