题目

某同学用氯酸钾和二氧化锰的混合物加热制取氧气时发生了爆炸，分析其可能的原因是（    ） A.管受热不均匀               B.气体发生装置漏气 C.二氧化锰中混有可燃性杂质   D.加热温度太高 答案：思路解析：由于加热时体系温度比较高，且产生了大量氧气，只要有可燃物，就可能发生爆炸。 答案：CEtiquette,or good manners,used to be the glue that held society together.1.Sadly,these days it has mostly gone by the wayside.This list is several best rules of etiquette that have now disappeared.Opening the DoorIn days gone by,a gentleman would always open doors for ladies.2.This has now almost entirely disappeared and it is not entirely the fault of the men.I have seen women laugh at men for opening a door for them.They seem to be confusing manners with chauvinism（大男子主义）.Writing Thank-You NotesIn days gone by,whenever a person received a gift,they would write a thank-you note as soon as possible.3. Parents would sit children down after a birthday or Christmas and coach them in their first thank-you note.It is a shame that gift giving has now become a virtual obligation and the idea of a thank-you note would be laughed at.4.We seem to have completely lost the concept of correct timing when it comes to parties these days.5.After all,a party normally has a guest of honor-this is usually the oldest woman present.It was considered extremely rude in the past to leave a party before the guest of honor-and once the guest of honor left,it was a signal to all that they should begin their own preparations to leave.A.Arriving on Time.B.Leaving at the Right Time.C.People leave with various excuses.D.It enabled people to get on well with each other.E.This rule was true even if the giver was a relative.F.It could be the lady they were driving,or a stranger.G.We've thrown away the concept of a guest of honor at will.