Defining-clause classification: select all statements that are true.
It can identify a subset of a larger group.✓Bonne réponse
It must always be enclosed by two commas.
Its object relative pronoun can sometimes be omitted.✓Bonne réponse
Every relative pronoun in it can be omitted.
Explication
A defining clause narrows the reference, normally has no surrounding commas, and may omit a relative element only when that element is an object. The claim that all relative pronouns can disappear is the closest false statement because subject relatives must stay expressed.