单项选择题
A.61.2dB B.37.2dB C.20.3dB D.13.2dB
A.57.5 B.44.4 C.37.8 D.31.3
A.6.1 B.18.2 C.23.1 D.34.5
A.8.0 B.12.0 C.15.0 D.18.0
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