什么情况下用has,什么情况下用have?

Question

什么情况下用has,什么情况下用have?

Answer 1

have和has在用于英语表达动词“有”的含义时,前者使用于第一人称、第二人称和各人称复数,has用于第三人称单数,同时它们也作为完成时态的助动词存在,其用法和做实义动词“有”的规则也是一样的.
助动词have的用法
1）have +过去分词,构成完成时态,例如：
He has left for London.他已去了伦敦.
By the end of last month,they had finished half of their work.
上月未为止,他们已经完成工作的一半.
2）have + been +现在分词,构成完成进行时,例如：
I have been studying English for ten years.
我一直在学英语,已达十年之久.
3）have+been +过去分词,构成完成式被动语态,例如：
English has been taught in China for many years.中国教英语已经多年.
动词have/has表示"有"时,它通常有三个含义:
A.表示"某人(在物质上的)所有."这种情况下不能用there be替换.如:
I have a new watch.我有一块新表.
He has a good friend.他有一个好朋友.
B.表示"某人或动物(在身体上的)长有".这种情况也不能用there be替换.
如:
She has blue eyes.她的眼睛是蓝色的.
A horse has two ears.马有两只耳朵.
C.表示"某物体(在结构上的)装有".这种情况可以用there be替换.如:
A clock has a round face.= There is a round face on a clock.
钟上装有一个圆型的钟盘.
That room has only two windows.= There are two windows in that room.
那个房间仅装有两扇窗户.
The school has 14 classes.= There are 14 classes in the school.
那个学校有14个班级.
D.另外,表示"某人手中有某物"时,也用have/has.例如:
Mary has a glass of water in her hand.玛丽手中端着一玻璃杯水.