问题 选择题

现有一块北方盐湖结晶析出的白色晶体,可能有Na2CO3、Na2SO4、NaCl中的一种或几种,为了证明其成份,加入试剂的正确顺序为(  )

①加水溶解②加入足量的硝酸钡溶液③加入足量硝酸④加入硝酸银溶液.

A.④②③①

B.①③②④

C.④②①③

D.①④②③

答案

先将样品加水溶解配成溶液,再加入足量硝酸,硝酸与碳酸钠反应能产生二氧化碳气体,所以加入硝酸,有气体产生,说明含有碳酸钠,且将碳酸钠除掉,在加入硝酸钡,由于硝酸钡与硫酸钠反应生成不溶于硝酸的白色沉淀硫酸钡,所以加入硝酸钡后有白色沉淀生成,说明含有硫酸钠,最后加入硝酸银溶液,硝酸银与氯化钠反应生成氯化银白色沉淀,且不溶于硝酸,所以加入硝酸银可鉴别是否含有氯化钠;所以顺序是:①③②④.

故选:B.

阅读理解

阅读理解。

     Different countries and different people have different manners. We must find out their customs so that

they will not think us impolite. Here are examples of the things that a person with good education does or

does not do.

     If you visit a Chinese family, you should knock at the door first. When the door opens, you will not move

before the host says "Come in, please." After you enter the room, you would not sit down until the host asks

you to take a seat. When a cup of tea is put on a tea table before you or sent to your hand, you will say "Thank

you" and receive it with two hands, not one hand, or they will think you have ill manners. Before entering a

house in Japan, it is a good manner to take off your shoes. In European countries, even though shoes sometimes

become very dirty, this is not done. In a Malay (马来人的) house, a visitor never finishes the food on the table.

He leaves a little to show that he has had enough. In England, a visitor always finished a drink or the food to

show that he has enjoyed it. This will make the host pleased.

1. According to the passage, people have different _______ in different countries.

A. manners

B. houses

C. families

2. It's _______ to sit down immediately after you enter the room in China.

A. important

B. polite

C. impolite

3. "ill manners" means _______ in Chinese.

A. 得体的举止

B. 无礼的举止

C. 文明的行为

4. Before entering the house in Japan, it is a good'manner to take off _______.

A. coats

B. gloves

C. shoes

5. Which is the best title of the passage?

A. Manners in Different Countries

B. People in Different Countries

C. Foods in Different Countries

多项选择题