1. which 先行词指的是物,在从句中作宾语
如：主句：The watch is beautiful.
从句：I bought the watch last week.
先行词是物：the watch, 在从句中作宾语,所以写成定语从句就是：
The watch which I bought last week is beautiful.
2. who 先行词指的是人,在从句中作主语和宾语
如：主句：The lady is very beautiful
从句：The lady is sitting under the tree.
先行词为人,the lady, 在从句中作主语,改写成定语从句就是：
The lady who is sitting under the tree is very beautiful.
3. whom, 先行词是人,且在从句中作宾语
如：主句：The lady is Miss Liu.
从句：My mother is talking with the lady.
先行词是the lady,在从句中作介词with 的宾语,所以改写成定语从句就是：
The lady whom(who) my mother is talking is Miss Liu.
4. whose 表示所有关系,相当于一个形容词性物主代词,后面要跟名词,表示所属关系
如：主句：The man lives alone.
从句：The man's wife died last year.
先行词是the man , 在从句中wife是属于the man's , 表示所属关系,所以改写成定语从句就是：
The man whose wife died last year lives alone.
如果你还看不懂,那你先要弄清楚句子成分,也就是主语,谓语,宾语,定语,状语,表语、
宾语补足语