主語
He was reading a book,which was about war.
He set free the birds happily,which was a celebration for his success.
You can find whatever you need at the shopping centre,which is always busy at the weekend.
The owner of the cinema needed to make a lot of improvements and employ more people to keep it running,which meant spending tens of thousands of pounds.
賓語
He was reading a book,which he had bought from London.
This isthe question which we’ve had so much discussion about.