Eg1:
There were two persons.
Both(= These two persons) were my friends.
Eg2:
Which of the two do you want?
I want both(= one and also the other).
Eg3:
Our head has ears on both sides, or an ear on each side.
1、Both sons study law.
2、Both the sons study law.
3、Both his sons study law.
4、Both these ( or those) sons study law.
5、Both of the sons study law.
6、Both of them study law.
7、His sons will both study law.
8、His sons both study law.
9、They both study law.
Both...and...可說是一個並列連詞,連接兩個平行或同等的東西,表示「.和.全」或「既.又.」等:
1、名詞 + and + 名詞
Both his hands and his feet were tied up.
2、介詞短語 + and + 介詞短語
The book was written both in Chinese and in English, both for boys and for girls.
3、形容詞 + and + 形容詞
She is both rich and intelligent.
4、動詞 + and + 動詞
She both listened and wrote.