某种部件使用在10000台计算机中,运行工作1000小时后,其中20台计算机的这种部件失效,则该部件千小时可靠度R为 (10) 。
A. 0.990
B. 0.992
C. 0.996
D. 0.998
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30()
A. must
B. might
C. could
D. needed
32()
A. but
B. then
C. as
D. therefore
33()
A. enjoy
B. mind
C. stop
D. help
27()
A. at most
B. at last
C. at least
D. at first