题目

下列物质中属于纯净物的是A．空气            B．粗盐          C．生铁        D．纯碱  答案：D解析:由一种物质组成的是纯净物，纯碱是纯净物，而空气中成分比较多，粗盐中除了氯化钠还有氯化镁等杂质，生铁中还有碳，所以都属于混合物，故选D  She was not______ frightened; in fact, she was nearly frightened to death.   A．a bitB．a littleC．at all D．much