不是说一个句子中必须有动词么.那这句话怎样理解 Swimming is a good exercise.动词就不能直接做主语吗?那这句话怎么理解:Break it up into smaller portions``````咋不说breaking it up`````

问题描述:

不是说一个句子中必须有动词么.那这句话怎样理解 Swimming is a good exercise.
动词就不能直接做主语吗?那这句话怎么理解:
Break it up into smaller portions``````咋不说breaking it up`````