1. It is+adj./n.十doing...
pity，use，a waste of time，bore，worth，difficult，funny，hard，nice，old，worth-
while, enjoyable, tiring, foolish, better, interesting等.例如:
It was difficult getting everything ready in time.
It is no use waiting here，let's walk home.
It is a waste of time trying to reason with such a stick-in-the-mud.
It's foolish behaving like that.
注意:important, essential, necessary等形容词不适用于上述结构。例如:
It's important to learn foreign languages. (IE)
It's important learning foreign languages.(误)
2. There be+no+doing...
There's no saying what he'll be doing next.
There's no telling what he's going to do.
There's no bearing such rude remarks.
There's no hiding of evil but not to do it.
注意:句中的动名词常带有宾语，意为“it is impossible to do".
有些动词后面只能接动名词作宾语。这类动词有:acknowledge, admit, confess, permit
avoid，escape, defer, delay, miss，postpone，put off, consider，contemplate.fancy
pate，appreciate，enjoy，risk，forgive，involve，include, look forward to，keep，mind，
stand, suggest, evade等。例如:
He denied having been there.
I couldn't risk missing that train.
She can't stand being kept waiting.
Ill appreciate hearing from you soon.
4. need，want, deserve，require，worth+doing结构
这一结构有被动含义。其中前面四个动词后面亦可接不定式的被动态to be done。例如:
The house wants repairing.
The house wants to be repaired.
The garden needs watering.
The garden needs to be watered.
His deeds deserve praising.
His deeds deserve to be praised.
Mary's grumbling annoyed her husband.
I felt annoyed at the noise of desks being closed and opened.
It's no use your pretending that you didn't know the rules.
The factory had to close down because of the equipment having been destroyed.