单项选择题
A.50~75dBμV B.65~85dBμV C.57~83dBμV D.60~80dBμV
A.40~70dBμV B.50~75dBμV C.57~83dBμV D.60~80dBμV
A.41dB B.43dB C.46dB D.53dB