I'll sit and clench my teeth and never tell you one thing.

我会咬紧牙关坐着，一件事也不告诉你。

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Some people clench or grind their teeth while they sleep, a condition called bruxism.

一些人睡觉时紧咬牙关或磨牙，这种情况称之为磨牙症。

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Toward the end of a fierce game, when everyone is nearly exhausted, who can clench ones teeth and hold on to the end is certainly a hero.

第三句说当激烈的比赛快要结束时，每个人都已精疲力竭，而咬紧牙关坚持到底的人就一定是英雄。 这一句是对图画的呼应--图上的运动员发出会心的微笑，他一定是在赛场上拼尽全力坚持到最后的人，可能正是他最后五分钟的进球为整个球队赢得了胜利。

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