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.