--你--Dianche湖这些天(可知道去了回来了）故排除A是的，我去了。那的水变得干净和那的山更美丽了（同志 beautiful 你都写错了） have been in指的是去某地同时待了一段时间have been to 只是强调“去过（某地）”的概念所以，have been in后面可以加时间状语，比如i ve been in UK for a month，但不能说I ve been to UK for a month，因为“去过”这一动作不可延续 所以综上所述 选B...
答案选B Have; been to根据下面的句子Yes,I have. The water is getting cleaner and cleaner and the mountains are more beartiful.的语境，证明回答者已经到过Dianche Lake这个地方，所以选B...
