有一读者问： 有人在一本考研指导书中写道：It is difficult后面接-ing形式。但我只见过“It is difficult+不定式”结构，如：
(1)It was difficult to put the tent up because of the wind.
在何种情况下后接-ing形式？
It is difficult之后可接不定式，亦可接v-ing,但前者比较强调动作或目的，如上述句（1），这种情况较为常见。后者则比较强调状态或持续性，实例如：
(2)It's very difficult writing because I feel that somebody is looking over my shoulder.
同样find it difficult后接不定式的情况亦较为常见，但其后亦可接-ing，如：
(3)He finds it extremely difficult being a single parent.
顺便提一下，形容词easy和difficult一样，其后亦可接-ing，如：
(4)It isn't easy being a teacher these days, you know.
