It is as if a single unimportant event set up a chain of rea

表语从句啊It is+表语（所谓的主+系+表） 表语用as if引导,翻译出来就是：
好像是一件无关紧要的小事引起了一连串的连锁反应
举几个例子吧
She looks as if she were ten years younger．
她看起来好像年轻了十岁.
It seems as if our team is going to win．
看来我们队要胜了.
It looks as if a tornado swept through your room.
好像有龙卷风席卷过你的房间.
It looks as if they're looking for something.
他们看起来好像在找什么东西.

定语从句啊