it 形式主语
can't be谓语动词
more important 表语
than介词
what is stated in the book宾语从句
that is the preciousness of time and the method to use it efficiently此句是真正的主语,它是主语从句,其中that是主语 is是谓语动词 the preciousness of time and the method to use it efficiently是表语不是说that引导主语从句时不做从句成分吗？这里的that是作具体成分的，不是引导词哈，因为这个that is the preciousness of time and the method to use it efficiently句子里面去掉that就少了主语了，当一个完整句子要做从句时，才需要用that这种不做成分的引导词来引导有问题，请追问，如满意，请采纳