—Please go on with your demonstration．
—But where was I?
—Well, you the two chemicals together．
A. tried to mix
B. were trying to mix
C. were trying mixed
D. had tried to mix
网友回答
A. tried to mix
(答案→)B. were trying to mix
C. were trying mixed
D. had tried to mix
解析：
根据句意是：--请继续你的演示。---到哪儿啦？---你想把两种化学物质混合起来。说明是刚才正在做…,用过去进行时。选B。