1．介词的省略
①一些与动词、名词或形容词搭配的介词常常可以省略，而保留介词后的动名词。常见的结构有：
have difficulty/trouble (in) doing sth.
be busy (in) doing sth.
spend some time(in) doing sth.
stop/prevent sb.(from) doing sth.
The heavy rain prevented him (from) arriving there on time.
大雨使得他没能近时到达那里。
He spent four hours (in) going over his lessons.
他花了4个小时复习功课。
