Examples

Here, the subject of the sentence is who, which replaces the name of the prankster who placed the whoopee cushion.

In this example, which is the subject of the sentence. It stands in for the specific sand castle about which the speaker is asking. Maybe it's one the amazing feats of sand sculpture featured at the annual Sand Sculpture Festival in Ostend, Belgium.

In this case, what is the subject of the sentence and replaces the actual score of the basketball game.