题目

—Where's the key？—I ________ know. A . aren't B . don't C . isn't D . am not 答案：B8．据性质决定用途，单质碳的下列用途最能体现常温下碳的化学性质不活泼的是（　　）A．用碳素墨写文件B．用金刚石割大理石C．用碳棒作电极D．用活性炭脱色制白糖