I am going ahead with B.
All others look out of scope & irrelevant.
Because Virtually all large metropolitan areas have zoos, the vacationers would like to visit some thing new i.e., pure aquariums rather than the ordinary zoos.
However, it is a tough one. I got the thought after a lot of time.
Please publish OA.
[quote="kok72"]In the United States, vacationers account for more than half of all visitors to what technically called â€œpure aquariumsâ€
Thnx & Rgds,