由that引导主语从句不能省略。请看例句： That he has told lies is quite clear. 他说了谎，这一点很明显。 “That he has told lies”是主语从句，在句中作主语，看作单数，谓语动词用单数。如果省去that，句子就成为：He has told lies is quite clear.句中便有了两个谓语，has told和is，这样就会引起理解上的混乱，显然是错句。 另外，由that引导的主语从句，往往被放在句尾，前面则用it充当形式主语。如： It goes without saying that he loves her at the first sight. 毫无疑问他对她一见钟情。 It is sheer luck that he survived the accident. 他在事故中逃过一劫纯粹是运气。