题目

---Sorry. I am late. ---It doesn't matter. The meeting ______ for just several minutes    A. has begun          B. has started      C. has been on        D. had been on 答案：C下列物质中，属于纯净物的是A.净化后的空气、氧化镁B.水和冰混合C.生锈的铁钉D.氯化钾、液氧