The speed of sound in water is roughly one mile a second----slower than through land but faster than through air. What is most important, different layers of ocean water can act as channels for sounds, focusing them in the same way a stethoscope does when it carries faint noise from a patient’s chest to a doctor’s ear. This focusing is the main reason that even relatively weak sounds in the ocean, especially low-frequency ones, can often travel thousands of miles.
【正确答案】：声音在水中的传播速度大约为每秒一英里，比其穿透陆地的速度要慢，但比其在空气中的传播速度要快。最重要的一点是，不同的海水层可用作声音的通道。它们可以把声音聚集于其中，就如同听诊器把病人胸腔中细微的杂音聚集起来传送给医生的耳朵那样。正因为海水层具有聚集声音的功能，海洋中一些相对较弱的声音，特别是低频声音，时常能够传播到数千英里之外的地方去。
