Adjective clauses that begin with one of the relative pronouns (e.g. who, whom, whose, which and that) are also called relative clauses. Relative clauses are used to modify nouns and some pronouns - to identify people and things, or to give more information about them.
- Those who have not yet registered should do so at once.
- It is a book which will interest children of all ages.
- I gave him an envelope, which he put in his pocket at once.
Relative clauses can also be introduced by that.
- Here is the book that you were looking for.