The　　 of the book makes it suitable for children.The man is considering the question as　　　.

A．simplicity;simplifier

B．simplicity;simplism

C．simplifier;simplism

D．simplism;simplifier

活性污泥法的基本设施为（）

A.曝气池

B.沉淀池

C.曝气池、沉淀池

D.曝气池、污泥池