Each time the swimmer's feet leave and enter the water, air comes along, increasing drag and reducing thrust.

无论什么时候，只要游泳者的脚从水面之上打入水中，空气就会随着脚进入水中，这些空气泡会产生阻力，而且还会减少推动力。

youdao

In the case of water regulation, the conversation may well continue to drag along slowly for some time to come.

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