单项选择题
A.6.9dB B.17.7dB C.28.8dB D.46.6dB
A.21.0dB B.20.0dB C.14.0dB D.10.0dB
A.5% B.3% C.2% D.1%
A.61.2dB B.37.2dB C.20.3dB D.13.2dB
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