关于sooftenhappen的用法Assooftenhappenswhenunderpressure,hetendstoconcentratemostofhisattentiononthesubjectmatter.这里"Assooftenhappenswhenunderpressure"是As引导的什么成分?happens表示这个是一个从句,

Question

关于so often happen的用法
As so often happens when under pressure,he tends to concentrate most of his attention on the subject matter.
这里"As so often happens when under pressure"是As 引导的什么成分?happens表示这个是一个从句,但又没有主语...难道是倒装句省略it 主语?

Answer 1

As相当于which,在句首不能用which只能用as,这是引导了个定语从句.
他趋向于把大部分注意力放在主要问题上,这在有压力的情况下经常发生.（在有压力的情况下他经常这样做）
He tends to concentrate most of his attention on the subject matter,as so often happens when under pressure.
再把so often放到happens后面就更容易理解了.