例句
Hold your breath for six seconds.
请你屏气6秒钟。
The operation takes only 30 seconds.
这个操作仅需要30秒钟。
Ultrasonic waves travel at around 300 metres per second .
超声波的传播速度约为每秒300米。
Hold your breath for six seconds.
请你屏气6秒钟。
The operation takes only 30 seconds.
这个操作仅需要30秒钟。
Ultrasonic waves travel at around 300 metres per second .
超声波的传播速度约为每秒300米。