问题 单项选择题

为一患者取印模时,先取一些粉红色糊状物置橡皮碗中,又取少许白色粉末一起调拌,1min后,调拌好的糊状物放在托盘内,迅速放在患者口内,3~5min后取出,糊状物已结固,变为白色

糊剂变硬,表明材料发生了

A.中和反应

B.螯合反应

C.可逆变化

D.置换和交联反应

E.物理变化

答案

参考答案:D

解析:
糊剂型与半水硫酸钙混合后的凝固反应是置换与交联。以藻酸钠为例,当藻酸钠与胶结剂硫酸钙作用时,藻酸钠中的Na+与硫酸钙中的Ca2+置换,生成硫酸钠和藻酸钙沉淀。交联反应是当钙盐取代两相邻分子的Na+离子时,产生两分子间的交相联结,使可溶性藻酸钠变为不可溶性藻酸钙凝胶弹性体。

解答题
阅读理解

阅读理解。

     Henry Ford was the first person to build cars which were cheap,strong and fast. He was able to sell

millions of models because be could produce them in large numbers at a time; that is, he made a great many

cars of exactly the same kind. Ford's father hoped that his son would become a farmer, but the young man

did not like the idea and he went to Detroit where he worked as a mechanic (机械师). By the age of 29, in

1892, he had built his first car. However, the car made in this way, the famous "Model T" did not appear

until 1908-five years after Ford had started his great motor car factory. This car showed to be well-known

that it remained unchanged for twenty years. Since Ford's time, this way of producing cars in large numbers

has become common in industry and has reduced the price of many goods which would otherwise be very

expensive.

1. Henry Ford was the man to build _____ cars. [ ]

A. cheap and strong

B. cheap and long   

C. fast and expensive

D. strong and slow

2. Ford was able to sell millions of cars, because _____. [ ]

A. he made many great cars

B. his cars are many   

C. he made lots of cars of the same kind

D. both A and B

3. The young man became a mechanic, _____. [ ]

A. which was his father's will

B. which was against his own will

C. which was against his father's will

D. which was the will of both

4. The "Model T" was very famous _____. [ ]

A. before 1908

B. between 1982 and 1908

C. before 1892

D. after 1908

5. Ford built his own car factory _____.[ ]

A. in 1903

B. in 1908

C. in 1913

D. in 1897