问题 选择题

能证明碳酸的酸性比硅酸强的事实是

A.二氧化碳溶于水生成碳酸,二氧化硅不溶于水也不能跟水直接反应生成硅酸

B.在高温条件下,二氧化硅跟碳酸钠反应,生成硅酸钠和二氧化碳

C.二氧化硅的熔点比二氧化碳高

D.二氧化碳通入Na2SiO3稀溶液中,生成白色胶状沉淀

答案

答案:D

D选项是较强的酸与较弱酸的盐溶液反应生成较强酸的盐和较弱的酸的复分解反应,这是该类复分解反应发生的条件。B选项是酸性氧化物与盐反应,而不是酸与碱反应,并且它是在高温下进行的熔融反应,由于CO2气体逸出才使得此反应进行。这与我们平常讲的复分解反应条件不同。

阅读理解

阅读理解。

     If you wish to become a better reader, here are four important points to remember about rate, or speed,

of reading:

     1. Knowing why you are reading-what you are reading to find out-will often help you to know whether

to read rapidly or slowly.

     2. Some things should be read slowly throughout. Examples are directions for making or doing something,

arithmetic problems, science and history books, which are full of important information. You must read such

things slowly to remember each important step and understand each important idea.

     3. Some things should be read rapidly throughout. Examples are simple stories meant for enjoyment, news,

and letters from friends, items, or bits of news from local, or hometown, paper, telling what is happening to

friends and neighbors.

     4. In some of your readings, you must change your speed from fast to slow to fast, as you go along. You

need to read certain pages rapidly and then slow down and do more careful readings when you come to

important ideas which must be remembered.

1. According to the passage, your reading speed depends on _____. [ ]

A. whether the reading material is easy or difficult

B. what you are reading

C. what your purpose in reading something is

D. both B and C 

2. If one wants to be relaxed by reading, one should take up _____. [ ]

A. a story book

B. a book on science and technology

C. news, letters from friends

D. some material full of information 

3. Which of the following readings should you read slowly and carefully?[ ]

A. Fairy tales.

B. Aesop's Fables.

C. Directions for use of a machine

D. An evening paper. 

4. Which of the following can best express the main idea of the passage? [ ]

A. How to decide your reading speed.

B. How to raise your reading speed.

C. How to improve your reading skills.

D. How to choose your reading materials.

单项选择题