谓碳素钢?何谓白口铁?两者的成分组织和性能有何差别?

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问题:

谓碳素钢?何谓白口铁?两者的成分组织和性能有何差别?

考点:机械工程铁碳合金铁碳合金题库
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阅读理解。

     People use money to buy food, books, bicycles and hundreds of other things which they need.  When

they work, they usually get paid in money.

     Most of the money used today is made of metal or paper. But in ancient times people used all kinds

of things as money. One of the first kinds of money was shells.

     In China, cloth and knives were used as money. Elephant tusks, monkey tails and salt were used in

some parts of Africa. Rice was also a kind of money used by the ancient in some islands.  Cows and

other animals were used as money, too.

     The first copper coins were made in china.  They were round and had a square hole in the center.

Different countries have used different metals (金属 ) as their money. Later, some countries began to

make coins of gold (金) and silver (银).

     But both gold and silver were heavy to carry when people needed a lot of coins to buy something

expensive. The Chinese were the first to use paper money. The first paper money looked more like a

note than the paper money used today.

Money has had an interesting history from the days of shell money till today.

1. People use money to buy______ .

A. food

B. bicycles

C. all the things they need

2. they usually get paid in money______ .

A. When people buy things

B. When people have holidays

C. When people work

3. In ancient times, people use as money______ .

A. cloth and knives

B. shells

C. all kinds of things

4. The first coins were made of______ .

A. gold

B. copper

C. paper

5. The first paper notes were used in ______ .

A. China

B. Africa

C. some islands

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C.①②④

D.①②⑤

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