les pronoms relatifs

La proposition subordonnée relative est liée à la proposition principale par un antécédent bien défini.

Comment les choisir :
Pour les personnes, on utilise "WHOM" : The man to whom Armstrong gave an autograph was my grandfather.
Pour les choses, on peut utiliser "THAT" ou l'omettre : The planet that they were talking about is Mars, ou The planet they were talking about is Mars.
Pour les choses, on utilise "WHICH" : The planet which is the most distant is Pluto.
Pour le temps, on utilise "WHEN" : There was a time when we knew little about space.
Pour le lieu, on utilise "WHERE" : They haven't found a planet where we could live yet.
Pour l'appartenance, on utilise "WHOSE" : Hawking, whose discoveries changed the world, died in 2018.
Pour dire "l'un(e) parmi...", on utilise "OF WHICH" : These planets, the best known of which is Mars, are millions of miles away.