1.that=which用于一般的定语从句中
eg:A book that I like it very much.=A book which I like it very much.
2.in which=where用于先行词为地点的定语从句中
eg:A small village where I will spend time with my parents.
3.who用于先行词为人的定语从句中
eg:A person who I am talking with is my mom.
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