如果潜入水下游泳，每隔二、三十秒他就得浮上水面呼吸一次新鲜空气。

If he goes down under the water, he has to come up for fresh air every twenty or thirty seconds.

youdao

如果潜入水下游泳，每隔二、三十秒他就得浮上水面呼吸一次新鲜空气。

If he goes down under the water, he has to come up for fresh air every twenty or thirty seconds.

youdao