的
De

的 is the possessive marker
Pronounced like “duh”

的 is the word used when you want express someone or something belongs to someone or something else.

¹ 她是谁？
她是李友。她是我的同学。
Ta shi shei?
Ta shi Liyou. Ta shi wo de tongxue.
Who is she?
She is Liyou. She is my classmate.

² 他是谁？
他是理查。他是我的老师。
Ta shi shei?
Ta shi Licha. Ta shi wo de laoshi.
Who is he?
He is Licha. He is my teacher.

³ 他是谁？
他是王明。他是我的学生。
Ta shi shei?
Ta shi Wangming. Ta shi wo de xuesheng.
Who is he?
He is Wangming. He is my student.

Remember, 的 always goes after the noun.
Noun + 的 + Noun.