Within the relative pronouns there are competing systems, not only in French but also in English. This means that different relative pronouns can be used:
Examples
The boy that crosses the street, is my brother.
The boy who crosses the street, is my brother.
And, we have a specialty in English that does not apply in French. In English the relative pronoun can be omitted, if it is a defining relative clause.
Example
The math teacher (that) I had last year, was really fun.
However, there are not only different options to choose from, but also different functions of relative pronouns.
