The energy is ____ makes the cells able to do their work. A. that B. which C. what
答案应该选C,what。虽然that也可以引起一个表语从句,但它不能既作表语从句中的主语又引起表语从句。而what却可以同时胜任这两点。本句中what既引起is后的表语从句,同时又作这个从句的主语。