A.
声波在真空中的传播速度等于 340 m / s " role="presentation" style="word-spacing: normal; box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; word-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;"> 340 m / s 340 m / s