A swimmer can't swim under water very long, because he must take a breath.

游泳的人不能在水下游太久，因为他必须呼吸。

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These remarkable pictures show how beluga whales help human visitors to swim under the thick ice.

以下这些不平常的图片展示了白鲸帮助人类访客在厚冰层下游泳的情景。

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Nicknamed a "monster in the waves", he was the first man to swim under four minutes in the 400-meter freestyle.

绰号叫“水中怪物”的他，是第一个在400米自由泳中游进4分钟的人。

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No one should swim alone and, if possible, always swim under the watchful eye of a certified lifeguard.

CNN: Water safety expert: 'Drowning doesn't just happen'

Adventurous travellers can swim under the waterfall via a natural swimming hole at the bottom of the falls.

BBC: Kauai��s hidden adventures

Visitors can swim under waterfalls or in natural pools, explore miniature caves and dive off a 5m-high wooden platform into the balmy waters below.

BBC: Livin�� la vida Bonito