即即to do to do ，其否定形式是，其否定形式是not to donot to do；不定式；不定式没有人称和数没有人称和数的变化。的变化。动词不定式:一. 不定式的句法功能1.Its normal to cry when we feel sad.(做主语)不定式做主语时,常用代词it 来代替不定式结构, 这时 it 被称为形式主语,而作为句子真正主语的不定式则被后置.往往放v.和adj.之后.e.g. To learn English well is not easy. = Its not easy to learn English well.Its + adj. (+for sb.) +to do sth.1. 不定式做主语：常用句型：Its + adj. (+for sb.) + to do sth. （对某人来说）做某事是怎样的形式主语 真正主语=To work out the problem is difficult for me.Its difficult for me to work out the problem.=Working out the proble
