He vowed that he would never do that again.

他发誓绝不再作那样的事。

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vow表示发誓。可在vow后加that引导出发誓的内容，也可用vow to do something。上句可写成：He vowed never to do that again.

例：
He vowed to do his best to win the game.
他誓言要全力以赴赢得比赛。