12)英语中的"单数"
1.主语的第三人称单数形式，即可用" he, she, it"代替的。如：
he, she, it， my friend, his teacher, our classroom, Tom, Mary's uncle
2.名词有单数名词和复数名词。如：
man（单数） - - - men（复数） banana（单数） - - - bananas（复数）
3.动词有原形，第三人称单数形式， - ing分词，过去式，过去分词。如：
go - - - goes - - - going - - - went - - - gone
work - - - works - - - working - - - worked - - - worked
watch - - - watches - - - watching - - - watched - - - watched
当主语为第三人称单数的时候，谓语动词必须用相应的第三人称单数形式。
如：
The boy wants to be a sales assistant.
Our English teacher is from the US.
Their daughter makes her breakfast all by herself.
