单项选择题
A.110m B.105m C.100m D.90m
A.0.496μs B.0.491μs C.0.490μs D.0.489μs
A.58.6dB B.40.1dB C.34.5dB D.18.6dB
A.6.9dB B.17.7dB C.28.8dB D.46.6dB
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