Difficult question.
To me the key was to realize that we are comparing A:current employees in major zoos toB:members of the general population who have spent a similarly large amount of time in close contact with animals .
If we were to compare current employees in major zoos with members of the general population, then of course A wouldn't be true as there is no reason why would greater percentage of general population develop animal-induced allergies. But we are interested only in that part
...
To me the key was to realize that we are comparing A:current employees in major zoos toB:members of the general population who have spent a similarly large amount of time in close contact with animals .
If we were to compare current employees in major zoos with members of the general population, then of course A wouldn't be true as there is no reason why would greater percentage of general population develop animal-induced allergies. But we are interested only in that part
...
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