--- Shall we ________John to help us with the project?

--- I don’t think it’s a good idea. He has too much work to do.

A．have

B．make

C．ask

D．let

不影响健康成年人身体健康的一次献血量是（　　）

A．1200--1500毫升

B．800--1000毫升

C．500--700毫升

D．200--300毫升