A young man was going to join the army (军队) and had to (41) a medical examination. The doctor was sitting at a desk when he came in. He said to the man, "Take your coat and shirt off and (42) on that chair.
The young man did so. The doctor looked at him for a moment without (43) up from his chair and then said, "All right. Put your clothes on again.
"But you haven’t examined me at ail!" the young man said in (44) .
"There is no need to do so," the doctor said with a (45) .
"When I (46) you to take your coat and shirt off, you heard me all right, so there is nothing wrong with your (47) . You saw the chair, so your eyes are (48) . You could take your clothes off and sit on the chair, so you must be in good health. And you understand what I told you to do and did it without a (49) , so you (50) healthy enough for the army.\

[A] told[B] tell[C] will tell

（1）家用液化石油气（主要成分是丙烷等物质）往往加入少量有特殊气味的物质（如二硫醇），请用分子观点解释下列问题：

①25m³的石油气可以装入0.024m³的钢瓶中．

②液化石油气泄漏时，能嗅到特殊的气味．

③液化石油气燃烧时，生成了水和二氧化碳．

（2）金属在日常生活中应用广泛，请利用金属的性质回答：

①铝元素在地壳中的含量远比铜大，但铝的利用却比铜晚得多，其主要原因是什么？

②假黄金首饰通常是用黄铜（含Cu、Zn和Pb的合金）制成的，从外观和密度上很难区别其真伪．请你利用家中现有条件，鉴别一件黄金首饰的真假．简述你的操作方法、现象及结论．