求助 ： 《白勇语法》 p019 11题

STOOLSY

[attachimg=613,587]84668[/attachimg]

就是这道题目，我问的有以下几个问题
1. in which 和 where 有什么区别 这里问什么说 phenomenon 只能 用 in which
2. “in which changes in ocean and atmosphere combine to allow the warm water that has accumulated”  这句话怎么理解
   changes 是当n.讲 作主语  combine 是谓语？

谢谢了~~