Critical Reasoning (CR) | Re: In the United States, vacationers account for more than half

In the United States, vacationers account for more than half of all visitors to what are technically called “pure aquariums” but for fewer than one quarter of all visitors to zoos, which usually include a “zoo aquarium” of relatively modest scope.

Which of the following, if true, most helps to account for the difference described above between visitors to zoos and visitors to pure aquariums?

(A) In cities that have both a zoo and a pure aquarium, local residents are twice as likely