21. The sun heats the earth, ___________ is very important to living things.
A. that B. what C. which D. where
22. He is a man with rich experience, from _______ much can be learned.
A. whom B. which C. where D. what
23. ---What do you think made Mar upset?
--- ___________ her new bicycle.
A. As she lost B. Lost C. Losing D. Because of losing
