11. 某聲波在空氣中傳播時的頻率為 \(f_1\),波長為 \(\lambda_1\),當折射進入水中傳播時的頻率為 \(f_2\),波長為 \(\lambda_2\),則下列的關係,何者正確?(A) \(f_1 = f_2\)(B) \(\lambda_1 = \lambda_2\)(C) \(f_1 > f_2\)(D) \(\lambda_2 > \lambda_1\)