题目

下列物质分别放入一密封的充满氧气的集气瓶里，充分燃烧后，冷却至室温，由于瓶内压强的明显减小，使瓶塞最难开启的是A．木炭             B．硫磺              C．蜡烛             D．红磷  答案：D解析:略 With two children _____ middle school, the parents are working hard.A．attendedB．being attended C．having attendedD．attending