单项选择题

电力供电的频率称为“工频”,我国的工频标准是( )° A.40 Hz B.50 Hz C.60 Hz D.70 Hz

A.40
B.50
C.60
D.70
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单项选择题
What is the speaker’s main topic?()

A.Effects of using mobile phones on healthy human cells.
B.Risks of developing cancer involved in the use of mobile phones.
C.Damage to healthy cells caused by the use of mobile phones.
D.The potential health hazards of mobile phones on humans.

单项选择题
管理层次和( )是影响行政组织结构形态的两个决定性因素。 A.管理目的 B.管理方法 C.管理幅度 D.管理技巧
A.管理目的
B.管理方法
C.管理幅度
D.管理技巧
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