不能,在名词性从句中,一般情况下,只有宾语从句中的that能省略,其它像主语从句,表语从句,同位语从句中的that在句中虽都不作成分,但都不能省略.
that分句在非正式语体中作表语时,其连词that通常可省略:
Our belief is (that) things will improve.
但若句子结构比较复杂,则that不可省略:
The energy debate is really just beginning. The only thing that is certain is 【that】 anybody who makes firm predictions about future will be in some part wrong.
——引自章振邦主编、上海译文1997《新编英语语法(第三版)》
不能 我还没有见过能够省略的