Time flies.

8'

变体:
1) 后接状语
Birds sing beautifully.

11'

An old man walked slowly down the hill.

7'

2) 后接介词短语
He went on holiday.

9'

They live in a small flat.

5'

3) 后接不定时式
We stopped to have a rest.

10'

4) 后接分词
I'll go swimming.

8'