Normal swells, known technically as gravity waves, are created by wind pushing the surface of the sea up and gravity then pulling it down, causing it to bounce.

一般的波浪，技术上被成为重力波，是由于风推动着海洋表面上升而后又在重力的作用下被拉向下方，这便会导致海水的回弹。

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And after the centre-back has played a match, his knee swells to three times its normal size.

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