问题 单项选择题 A1/A2型题

口腔内金属的腐蚀主要是指()

A.孔蚀

B.缝隙腐蚀

C.应力腐蚀

D.电化学腐蚀

E.晶间腐蚀

答案

参考答案:D

解析:口腔内金属的腐蚀主要是电化学腐蚀,这是因为口腔内唾液是弱电解质溶液,摄取的食物中可能含有大量的弱酸、弱碱性物质和盐类,停留于牙间的食物残屑分解而发酵产生的有机酸等均可构成原电池而产生电化学腐蚀。口腔内金属表面的裂纹、铸造缺陷及污物的覆盖等,能降低该处唾液内的氢离子浓度而成为原电池正极,处于高阳离子浓度唾液中的金属则为负极,构成的原电池可使负极金属腐蚀。故答案为D。

阅读理解

阅读理解。

     Three people were walking along a street, first a big man, then a beautiful woman, and then an old

man. The first two went round a corner. Suddenly the old man saw a piece of paper on the ground. He

picked it up. The old man found it was five pounds. A few seconds (秒) later, the young woman came

back. She was crying. "I have dropped five pounds," she said. "Don't cry," said the old man, "Here it is."

The young woman thanked him and went away. After a few seconds, the big man came back. He was

looking for something. Suddenly a window opened and a small man looked out. "I saw five Pounds fall

 from your pocket," he said, "but that man gave it to a young woman." The big man was very angry.

The old man was very afraid and gave him another five pounds. When the old man had gone, the young

woman came back to get her one pound thirteen shillings (先令) and four pence (便士), and the small

man came out to get the same money.

     (one Pound = twenty shillings; one shilling = twelve pence)

1. Why did the old man pick up the paper? Because he _____. [ ]

A. wanted to keep it for himself

B. needed money very much

C. knew it was not money

D. wanted to know what it was

2. The old man was _____ another five pounds to the big man. [ ]

A. too afraid to give

B. good enough to give

C. so afraid that he had to give

D. such a kind man that he gave

3. Who knew each other? [ ]

A. The young woman and the old man.

B. The old man and the small man.

C. The young woman and the big man.

D. The old man and the big man.

4. Which following is true? [ ]

A. The small man lost the money.

B. The big man lost the money.

C. The old man threw the money.

D. Either the young woman or the big man threw the money.

5. How much did the small man get? He got ____. [ ]

A. as much as the young woman

B. nothing at all

C. more than the young woman

D. less than the big man

单项选择题