题目

 It has come to be realized ______ particular matters in the air expose us to life’s real danger. A. what      B. which          C. when               D. that 答案：  D下列哪些性质可以鉴别以下各种物质，请将有关的序号填在横线上：①颜色  ②状态  ③气味  ④味道  ⑤硬度糖水和盐水 ；氧气和水 ；铜和铝 ；金刚石和玻璃 ．