不是说可以省略，而是不用that吧，主语从句除了that还可以用不定,不定式短语,动名词以及动名词短语充当真正主语。
例如
It is very useful to learn English so well
It is the police's duty to protect the peope's life and properties
It is not so effective learning English without practising.
It is his duty taking good care of all his children.
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024