Tourism, it brings in money to a country, can also result in damage to the World
Heritage sites there.
A. once
B. while
C. if
D. as
网友回答
A. once
(答案→)B. while
C. if
D. as
解析：A. once一旦，B. while虽然，当…时候，然而，C. if如果，D. as正如，句意：--旅游业虽然给一个国家带来收益，也会给这里的世界遗产带来破坏。所以选B。