题干

下列除去杂质的方法正确的是(   )

①除去乙烷中少量的乙烯:光照条件下通入Cl2,气液分离

②除去乙酸乙酯中少量的乙酸:用饱和碳酸钠溶液洗涤,分液、蒸馏

③除去C2H6中少量的C2H4:气体通过盛有酸性高锰酸钾溶液的洗气瓶

④除去乙醇中少量的乙酸:加足量生石灰,蒸馏.

A:①②

B:②④

C:③④

D:②③

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答案(点此获取答案解析)

B

同类题4

阅读下列短文,然后从每小题A.B.C.D四个选项中选出能回答所提问题或完成所给句子的最佳答案。

    It seems that school children all over the world complain (抱怨) about their school food. What do students of your age eat for lunch at school in other countries?

Japan

    High schools have dining rooms. They serve everything from noodles to rice, but not burgers and chips. Other children bring food from home, such as cold rice balls, meat or fish, pickles (泡菜) and vegetables. Twice a year parents are invited to have a taste of the food.

United States

A typical menu from a US school is made up of a hamburger with fried potatoes or roast chicken, lettuce and pickles, fruit and cookies. School lunches must also provide at least one third of the daily amount (总量) of necessary nutrition (营养), such as, vitamin A, vitamin C and calcium (钙).

Australia

    Meat pies, sausage rolls (香肠卷) and hotdogs are all traditional dishes in Australian school shops. But as the country pays more attention to children's health, healthier foods have started to appear on school menus. Many schools have used a traffic light system. The sale of red labeled c标注) foods, including cookies, chocolate and soft drinks. Is served only twice a week. Healthier green labeled foods such as sushi, sandwiches, corn and watermelons, however, are available every day.

South Africa

    Most of South African schools do not serve meals at all. Classes end at l; 30 p. m. and students get their own lunches. Many students bring food from home, usually sandwiches.

      Fast food and fried food sell the best among students. As a result, it has caused a rise in obesity c肥胖) among children. But as more people began to realize that being too fat may cause different kinds of serious illnesses, some schools in towns have led the way towards better nutrition. Now students at these schools are offered lunches of porridge with vegetables, such as cabbage, onions, beans, carrots and tomatoes.