Relative clauses (betrekkelijke bijzin)
Sam,
who lives next door, is my best friend.
The jewellery, which is handmade, looks great.
Dancing is a hobby that takes up a lot of my time.
The gym which we always practise in is closed.
The instructor, who you told me about, is really nice.
The instructor, about whom you told me, is really nice.
The girl, whose passion is dancing, went to the club.