air hole是什么意思

用法例句

It puts forward that inverted breaststroke and inverted crawl in synchronization may help beginners to master the way of change breath very conveniently.

本文通过对比实验,指出掌握水中换气方法是学习蛙泳技术及其他泳姿动作的关键,提出同步的反蛙泳和仰泳练习,可以使初学者快捷地学会蛙泳的换气动作。