声波的传播速度主要取决于（）。
A、脉冲长度
B、频率
C、声波的传播介质
D、上述都不对
参考答案：C
It is a truth universally ______ that a single and rich man must be in want of a wife.
A．achnowledging
B．achnowledged
C．be achnowledged
D．to achnowledge
