关于necessary.it is necessary to do sth.it is nec
问题描述：
关于necessary.it is necessary to do sth.it is nec
关于necessary. it is necessary to do sth. it is necessary to doing sth. 两者有什么区别?什么时候用to do .什么时候用 to doing?请回答,
答
it is necessary to do sth.当中it是形式主语,it=to do sth,to do sth才是真正的主语成分,to do sth是不定式.
it is necessary to doing sth.当中it是真正的主语成分,to doing sth是介词加名词,是句子的表语补足语,是补语成分.还是不很清楚，有没有例证？有的。IT IS NECESSARY TO STUDY。学习很重要。WE SHOULD READ BOOKS。IT IS NECESSARY TO STUDYING。我们要读点书。读书对于增进学习能力来说是必须的。我懂了，谢谢！