通常用that ,what,which,how等等疑问词作引导词构成宾语从句,状语从句,主语从句,定语从句等等。英语作文里面用从句是加分点!那就是主语从句.如:That the earth gose aroud the sun is truth一个英语句子中选什么做主语;名词,代词,数词,非谓语to do, doing,主语从句,he is a doctor。my mother is cooking , to see is to believe. Getting up rarly is difficult for him ,whether we will go is not decided。it做形式主语,it is hard for me to solve them