武装部队保持高度警惕，以防发生任何报复行为。

The armed forces were on high alert to guard against any retaliation.

《柯林斯英汉双解大词典》

你应该在家里放一个急救箱，以防发生事故。

You should keep a first-aid kit in your home just in case there is an accident.

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我们点起了蜡烛，营造好气氛，还准备了一支手电筒，以防发生什么差错。

We lit candles to set the mood and had a flashlight in the ready in case anything went wrong.

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We have, for example, bomb drills just in case something happens people think it's right When thing happens once and you move on, go back to life, just as something goes wrong and then you move on.

例如，我们有，炸弹演习以防发生什么事情,人们认为这是应该的,发生了一件事，你要继续正常的生活，正如某事出了点问题，然后你继续前行。

普林斯顿公开课 - 人性课程节选