求翻译：Sirens are generally higher in pitch than horns or diaphones, but are very variable in tone and power. Reeds are weak, high-pitched fog singles, often used at harbour entrances ,and Explosive signals are self-explanatory. Bells,Gongs and whistles are used mainly on buoys, where they may be operated either by the rocking or heaving motion of the sea, or by machinery. Bells and gongs are self-explanatory, but whistles are often much lower in pitch than one might expect if you have not heard one before.是什么意思？

待解决 悬赏分：1 - 离问题结束还有