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【简答题】
为了防止意外,在矿内同时设有两报警系统 A 与 B ,每种系统单独使用时,其有效的概率系统 A 为0.92,系统 B 为0.93,在 A 失灵的条件下, B 有效的概率为0.85,求: ( 1 )发生意外时,这两个报警系统至少一个有效的概率 ( 2 ) B 失灵的条件下, A 有效的概率
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【单选题】He is said___________a book on the history of Chinese tone bridge , but I don’t know if he has finished it.
A.
to have written
B.
to be writing C . having writing D writing
【单选题】______ he wanted to go out with his friends at the weekend, he had to stay behind to finish his assignment.
A.
Much though
B.
Much as
C.
As much
D.
Though much
【单选题】No sooner______this talk than he was surrounded by the workers.
A.
he finished
B.
did he finish
C.
had he finished
D.
after he finished
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