单项选择题
A.2~3V B.3.5~4.5V C.5~6V D.6.5~7.5V
A.20Hz~20kHz B.31.5Hz~12.5kHz C.40Hz~16kHz D.50Hz~16kHz
A.2V±0.5V B.4V±0.5V C.5V±0.5V D.10V±0.5V