题目

When I passed Mr Black’s office, he ______ our exam results with the head teacher.        A. discusses                 B. is discussing        C. discussed                D. was discussing  答案：D6．与根吸收矿质元素离子关系最密切的生理活动是（　　）A．光合作用B．渗透作用C．蒸腾作用D．呼吸作用