7. The intensity level of sound at 10 m away from a point source of sound is 80 dB. What will be the intensity level at 20 m away from this source?
(A) 90 dB
(B) 77 dB
(C) 74 dB
(D) 70 dB
(E) 60 dB
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統計: 尚無統計資料
統計: 尚無統計資料