试题与答案

计算氟利昂12(R12)和氨(R717)制冷剂在冷凝温度tk=30℃,蒸发温度 t

题型:单项选择题

题目:

计算氟利昂12(R12)和氨(R717)制冷剂在冷凝温度tk=30℃,蒸发温度
to=-15℃时进行循环的理论制冷系数,以及在上述tk、to温度条件下,采用回热循环(压缩机吸气温度t1’=5℃)的理论制冷系数,则两种制冷剂采用回热循环制冷系数的变化情况为( )。

A.R12采用回热循环制冷系数提高
B.R717采用回热循环制冷系数提高
C.R12采用回热循环制冷系数下降
D.R717采用回热循环制冷系数不变

答案:

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参考答案:A解析: 关系数据库标准语言SQL中邪。 LECT语句的功能是查询。COUNT是用于计数的函数; FROM说明要查询的表;WHERE说明查询条件;DIS。 TINCT去掉结果中的重复值。

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                                                       My Garden by Nelson Mandela

     In early 1977, the authorities (当局) announced the physical labour and arranged some kind of work for

us to do in the courtyard. The free time also allowed me to hunt what became two of my favorite hobbies in

Robben Island-gardening and tennis.

     To survive in prison, one must develop ways to take satisfaction in one's daily life. One can feel fulfilled

(充实) by washing one's clothes so that they are particularly clean. Just as one takes pride in important tasks

outside of prison, one can find the same pride in doing small things inside prison.

     Almost from the beginning of my sentence on Robben Island, I asked the authorities for permission to

start a garden in the courtyard For years, they refused without offering a reason But finally they gave in, and

we were able to cut out a small garden on a narrow patch of earth against the far wall.

     The soil in the courtyard was dry and rocky. In order to start my garden, I had to remove a great many

rocks to allow the plant room to grow.

     The authorities supplied me with seeds. At first, I planned tomatoes and onions, because these plants did

not require rich earth or constant care. The early harvests were poor, but they soon improved.

     I began to order books on gardening. I studied different gardening techniques and types of fertilizers (肥

料). I did not have many of the materials the book discussed, but I learned by trial and error (反复实验). For

a time, I tried to grow peanuts, and used different soils and fertilizers, but finally I gave up. It was one of my

few failures.

     A garden was one of the few things in prison that one could control. The process of planting a seed,

watching it grow, taking care of it and then harvesting it offered a simple but long-lasting satisfaction. The

sense of being the owner of the small patch of earth offered a small taste of freedom.

1. Mandela's hobbies on Robben Island were ____.

A. hunting and physical labour

B. gardening and tennis

C. washing his clothes

D. gardening techniques and types of fertilizers

2. When did Mandela ask the prison authorities for the permission to start a small garden?

A. Soon after 1997.

B. Some time in early 1977.

C. Almost as soon as he went to prison there.

D. Long after he went to prison there.

3. Why did Mandela wash his clothes especially clean although he was in prison?

A. To show he could do it as well as others.

B. To get some sense of pride and satisfaction from it.

C. To show others that he preferred to be clean.

D. To gain the authorities' permission to start a garden.

4. Hard as he tried, he failed ____ at last. 

A. to order books on gardening

B. to grow tomatoes and onions

C. to grow peanuts

D. to get the same pride inside prison.

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