题目

．下列说法正确的是                                                    （     ）  A．吸入雾霾、PM2.5等对人体健康没有危害 B．电解水实验中正极和负极产生的两种气体质量比为1：2 C．呼出的气体中含量最多的气体是二氧化碳 D．在用红磷测定空气中氧气的体积分数时，充分反应后，需将装置冷却至室温再打开弹簧夹读数，否则测量结果偏低 阅读理解 　　I was on a train the other day, in an empty compartment, and I wanted to read the last part of a detective story．Then the door opened and a mother with two small children asked me, “may we sit here, Madam?” at first I wanted to say, “well, actually, I’m reading an exciting book and I’d like to finish it．Could you find another compartment?” 　　But of course I said, “yes, certainly,” I still had not finished that book．Unfortunately, I found it very difficult to say “No” to those magic words “May I…” or “would you mind if…” 　　Of course people usually ask permission to do quite harmless things, like using the telephone, turning the light on, opening the window and things like that．But then there are some funny requests．Some people even ask if they may wash their hands or take their coats off．On the other hand, very few smokers will bother to ask permission to smoke! 　　But what about those difficult requests like, “Do you mind if I come round for a cup of coffee?” or “Is it all right if I bring the children to the party? They are very good really．” The trouble is, I just don’t have the nerve to refuse．Well, do you? (1) The writer describes those requests as “magic words” because they ________ [　　] A． are amusing B． are harmless C． always work D． are easily understood (2) According to the writer, asking permission to smoke is ________ [　　] A． a foolish request B． a difficult request C． an unnecessary request D． none of the above (3) Difficult requests are those which ________ [　　] A． are never permitted B． are never refused C． make other people uneasy D． make other people unfortunate (4) Which of the following may express the main idea of the passage? [　　] A． I’m a polite person B． Requests of different kinds C． How to make a request D． How to answer a request