在加有滤波电容的整流电路中，二极管的导通总是（）1800
A.大于
B.小于
C.等于
参考答案：B
标准品和质控品的不同点是什么?理想的标准品和质控品应具备什么特征?
Packet-switching wireless networks are preferable (1) when transmissions are (2) bemuse of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network.
5（）
A．point
B．start
C．length
D．end
