He ran so fast that I couldn't catch up with him.
他跑得太快赶不上他.

说得对.这确实是一个“主系表”句型.当表语是表示人的心理状态的形容词（也可以是表心理状态的动词的分词,大多是过去分词）时,后面接从句,不定式短语或介词结构等说明心理状态产生的原因.
如；I'm sorry to have kept you waiting for a long time.
He is proud that h搜趣网is daughter has been admitted to a famous university.

it's time that we begin our work.(it's time .....是“正是做什么的时间”的意思)
it's important MRbRFFzNBethat this application is filled.
itwww.souquanme.com9;s said that Mike has been killed.（it's said是“据www.souquanme.com说。。。。”的句型）
it's working that we persuade him.(我们劝说他似乎正在起作用)——这里要注意，不及务动词是没有被动态的，因此只能够用ing形势

She said so slightly that I couldn't hear clearly.
She cried loudl//www.souquanme.comy that we could hear in the distance.
She worked well that I admired her.