帮忙解释一下这个cr

samgxs

In the US, 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.
下面哪个解释difference?
Virtually all large metropolitan areas have zoos, whereas only a few large metropolitan areas have pure aquariums.

顺便解释一下！

redli

那句话的意思：几乎所有大都市都有动物园（里面也有水族馆），但只有少部分大都市有
“纯水族馆）
这题的关键在两个区别：
1）vacationers：可理解为从外地来的参观者
   visitors：含外地和本地的参观者
2）zoo aquarium：动物园里的水族馆（一般规模小，品种少）
   pure aquariums：专业的大型水族馆