.as,which引导的定语从句,修饰整个句子
1）as引导的定语从句可以放在句首,句中,句末,从句中的动词常常是know,understand,see,report,---带有一种众所周知的意思
The earth is round,as is known to us all.地球是圆的,这一点大家都知道.= As is known to us all,the earth is round.= The earth,as is known to us all,is round.
2）which引导的这样的定语从句只能放在从句后,动词没有限制.
He didn`t pass the English exam,which made his parents disappioted.他没有通过英语考试,这使他的父母很失望.