下列有关溃疡性结肠炎的X线钡灌肠表现中，错误的是A．肠管狭窄短缩 B．多发溃疡 C．

漂白剂亚氯酸钠（NaClO₂）在常温与黑暗处可保存一年。亚氯酸不稳定可分解，反应的离子方程式为：5HClO₂＝4ClO₂↑＋H^＋＋Cl^－＋2H₂O。向NaClO₂溶液中滴加H₂SO₄，开始反应缓慢，随后反应迅速，其原因是 [ ]

A.  在酸性条件下亚氯酸的氧化性增强    

B.  溶液中的H^＋起催化作用

C.  ClO₂逸出，使反应的生成物降低      

D.  溶液中的Cl^－起催化作用

2002年我国第三产业在国内生产总值中的比重为多少( )

A．14.5%

B．51.7%

C．33.7%

D．46.4%

按照《产品质量法》的规定，（）是生产者承担产品责任的前提。

A.产品使用不当

B.产品过期销售

C.产品存在缺陷

D.产品被假冒

开展干细胞研究对人类有何积极意义？

阅读理解。

     Like fine food, good writing is something we approach with pleasure and enjoy from the first taste to

the last. And good writers, like good cooks, do not suddenly appear full-blown. Quite the opposite, just

as the cook has to undergo a particular training, mastering the skills of his trade, the writer must sit at his

desk and devote long hours to achieving a style in his writing, whatever its purpose is-schoolwork, matters of business, or purely social communication.

     You may be sure that the more painstaking the effort, the more effective the writing, and the more

rewarding.

     There are still some faraway places in the world where you might find a public scribe to do your

business or social writing for you, for money. There are a few managers who are lucky enough to have

the service of that rare kind of secretary who can take care of all sorts of letter writing with no more than

a quick note to work from. But for most of us, if there is any writing to be done, we have to do it

ourselves.

     We have to write school papers, business papers or home papers. We are constantly called on to

put words to papers. It would be difficult to count the number of such words, messages, letters, and

reports put into mails or delivered by hand, but the daily figures must be extremely large. What is more,

everyone who writes expects, or at least hopes whatever he writes will be read,    from first word to last,

not just thrown into some "letters-to-be-read" files or into a wastepaper basket. This is the reason we

bend our efforts toward learning and practicing the skills of interesting, effective writing.

1. In this passage, good writing is compared to fine food because _______.

A. both are enjoyable     B. both are hard to learn

C. both are necessary to lifeD. both take a long time to prepare

2. according to the passage, which of the following statements is true?

A. Writing skills are less important than experience.

B. A good writer should have his own way of writing.

C. A good writer should learn to write all kinds of articles.

D. The more efforts one makes, the more money one can earn.

3. The author thinks that the most important reason for us to practice writing skills is _______.

A. to earn our living        

B. to attract others to read

C. to do daily reports easily

D. to become good secretaries

4. The purpose of the author in writing this passage is to _______.

A. comment and blame  

B. introduce and describe

C. explain and persuade  

D. interest and inform