that與after？

這就是一個非限制性定語從句,由which引導應該說after which 可以換成after it/that 這里的it和that應該代指前面整個句子,要用after that 的話就要用逗號 ,如We stood around him and watched attentively,after that, we started try by ourselves(我們圍著他并聚精會神地看著,之后我們開始自己嘗試)是定語從句的,先行詞看成前面整個句子,介詞后不能跟that