Is Mr.Douglas a friend of _____?

问题描述:

Is Mr.Douglas a friend of _____?
Is Mr.Douglas a friend of your father?
为什么不是your father's?

of 直接+名词,加了名词就不用什么's了,可以看成of就是表示是XXX的XXX,和's一样,A is B of C就是说A是C的B.
或者写成is Mr.Douglas your father's friend?
明白了吧.