超纯水的电导率是（　 　　）。 A: 小于0．1uS/cm　　 B: 0．5-2uS/cm　 C: 2-4uS/cm　　　 D: 50-500uS/cm

电子数字频率计可测周期范围的最大时间，一般为（）。 A: 0.1us B: 1us C: 10s D: 1s

已知某信号的频率是100kHz，则该信号的周期是多少？ A: 0.01s B: 0.1ms C: 0.01ms D: 0.1us

In a certain year, the world’s total export value was 1.6 trillion US dollars, and import value was 1.7 trillion US dollars, so the total international trade of that year was （ ） A: $ 3.3 trillion dollars B: $ 1.6 trillion dollars C: $ 1.7 trillion dollars D: $ 0.1 trillion dollars

Are there enough books for ____? A: three us B: us three C: all us D: the three us

______ agrees to your plan. A: Anyone of us B: No one of us C: None of us D: Someone of us

Mr. Yang ______. A: teaches math us B: teaches us to math C: teaches math to us D: us teaches math

已知一脉冲信号其周期为1us，经过一个10分频器后，输出脉冲的周期为（）。 A: 0.1us B: 10us C: 20us D: 0.05u

已知一脉冲信号其周期为1us，经过一个10分频器后，输出脉冲的周期为（）。 A: 0.1us B: 10us C: 20us D: 0.05us

What does sleeping help us? A: It helps us stay healthy. B: It helps us improve our memory. C: It helps us reduce stress. D: It helps us lose weight.