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问题 单项选择题

人机系统组成的串联系统中，如果人的操作可靠度RH=85%，机器设备可靠度RM=97%，则人机系统可靠度RS=( )。

A．82.45%
B．12%
C．45.3%
D．17.55%

答案

参考答案：A

解析：本题考查的是对串联人机安全系统的理解
人机系统组成的串联系统可按下式表达：
RS=RH·RM
式中RS——人机系统可靠度；
RH——人的操作可靠度；
RM——机器设备可靠度。

单项选择题

热水采暖管道的循环压力，应根据管道内的容许流速及系统各环路的压力平衡来决定，一般宜保持在（）右。

A.10～30kPa

B.10～40kPa

C.20～30kPa

D.20～40kPa
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单项选择题

A punctual person is in the habit of doing a thing at the proper time and is never late in keeping an appointment.
The unpunctual man, on one hand, never does what he has to do at the proper time. He is always in a hurry and in the end loses both time and his good name. A lost thing may be found again, but lost time can never be regained. Time is more valuable than material things. In fact, time is life itself. The unpunctual man is for ever wasting and mismanaging his most valuable asset as well as other’s. The unpunctual person is always complaining that he finds no time to answer letters, or return calls or keep appointments promptly. But the man who really has a great deal to do is very careful of his time and seldom complains of want of it. He knows that he can not get through his huge amount of work unless he faithfully keeps every piece of work when it has to be attended to.
Failure to be punctual in keeping one’s appointments is the sign of disrespect towards others. If a person is invited to dinner and arrives later than the appointed time, he keeps all the other guests waiting for him. Usually this will be regarded as a great disrespect to the host and all other guests present.
Unpunctuality, moreover, is very harmful when it comes to do one’s duty, whether public or private. Imagine how it would be if those who are put in charge of important tasks failed to be at their proper place at the appointed time. A man who is known to be habitually unpunctual is never trusted by his friends or fellow men.

According to the third paragraph, when you are invited to dinner, you should arrive there ______.

A. after other guests have arrived
B. before all other guests
C. at the appointed time
D. after the host has got things ready
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