计量基准通常分为国家计量基准、（）和工作计量基准三类，也分别称作一级、二级、三级基准

现有A、B、C、D四种元素，A元素形成的—2价阴离子比氦原子的核外电子数多8个，B元素与A元素可组成一种化合物E，为淡黄色固体，该固体遇到空气能生成A的单质；C为原子核内有12个中子的金属元素，当2.4gC与足量热水反应时，在标准状况下放出气体2.24L，C形成正二价阳离子；D元素原子的M层上有7个电子。

（1）写出B、C两种元素的元素名称：B      ，C      ，指出D在周期表中的位置                     。

（2）D的气态氢化物与H₂S、HF的稳定性由强到弱为           （用化学式表示）。

（3）写出淡黄色固体E的电子式            ，其中含有的化学键为            。

（4）钾元素与B元素位于同一主族，钾元素与A元素可形成K₂A、K₂A₂、KA₂等多种化合物，其中K₂A₂和KA₂和CO₂均可发生反应（反应与淡黄色固体E和CO₂的反应类似），写出KA₂与CO₂发生反应的化学方程式                         。K₂A₂、KA₂在医院、矿井、潜水、高空飞行中常用作供氧剂，为了维持气压稳定可以使用过氧化钾和超氧化钾的混合物使吸收的CO₂与生成的O₂体积相同（同温同压）,则它

们的物质的量之比为        。

初步诊断

A．脑震荡
B．脑挫裂伤
C．脑供血不足
D．脑水肿
E．脑疝

阅读理解。

                                                                      Paragraph 1

      Scientists have learned a lot about the kinds of food people need. They say that there are several kinds of

food that people should eat every day. They are: (1) green and yellow vegetables of all kinds. (2) citrus (柑桔)

fruits and tomatoes; (3) potatoes and other fruits and vegetables; (4) meat of all kinds, fish and eggs; (5) milk

and foods made from milk; (6) bread or cereal (谷类), rice is also in this kind of food; (7) butter, or something

like butter.

                                                                      Paragraph 2

     People in different countries and different places of the world eat different kinds of things. Foods are

cooked and eaten in many different kinds of ways. People in different countries eat at different times of the

day. In some places people eat once or twice a day; in other countries people eat three or four times a day.

Scientists say that none of the differences is really important. It doesn't matter whether foods are eaten raw

(生的) or cooked, canned or frozen. It doesn't matter if a person eats dinner at 4 o'clock in the afternoon or

at eleven o'clock at night. The important thing is what you eat every day.

                                                                      Paragraph 3

     There are two problems, then, in feeding the large number of people on earth. The first is to find some

ways to feed the world's population so that no one is hungry.

     The second is to make sure that people everywhere have the right kinds of food to make them grow to

be strong and healthy.

1. According to the scientists, which of the following groups of food is the healthiest for your lunch? [ ]

A. chicken, apples, cereal, cabbages

B. potatoes, carrots, rice, bread

C. oranges, bananas, fish, tomatoes

D. beef, pork, fish, milk

2. It is important for people to eat _____. [ ]

A. three times a day

B. dinner at the right time

C. cooked food all the day

D. something from each of the seven kinds of food every day

3. Which of the following is NOT true? [ ]

A. People in some places don't have enough to eat.

B. There are too many people in the world.

C. One of the problems is that no one is hungry.

D. The scientists are trying to make people grow to be strong and healthy.

4. If there is Paragraph 4, what do you think is going to be talked about? [ ]

A. When people should eat

B. What to do with the two problems

C. How to cook food in different ways

D. Why people eat different kinds of food

古希腊一位著名的政治家曾说过：“我们的制度之所以称为民主政治，因为 * * 是在全体公民手中，而不是在少数人手中。”这位历史人物是（   ）

A．汉谟拉比

B．伯里克利

C．汉谟拉比

D．凯撒

下图是温度和压强对X+Y2Z反应影响的示意图。图中纵坐标表示平衡混合气体中Z的体积分数。下列叙述正确的是（   ）

A．X、Y、Z均为气态

B．恒容时，混合气体的密度可作为此反应是否达到化学平衡的判断依据

C．升高温度时增大，减小，平衡向右移动

D．使用催化剂Z的产率增加