- Does the meaning of the sentence change if you delete the clause? --> Use THAT.
- If the meaning doesn't change, does the clause give extra info about the subject? --> Use WHICH.
The Grand Canyon is a U.S. National Park that/which is in Arizona.
(er is maar 1 National Park met de Grand Canyon)
My brother doesn't like sports that/which are played indoors.
(er zijn meerdere mogelijke indoor sporten)