I'll keep the letter as a precaution.

　　我要保存這封信，以防萬一。

　　I had taken the precaution of doing a little research before I left London

　　我已在離開倫敦前進(jìn)行了準(zhǔn)備，做了些調(diào)查研究。

　　Could he not, just as a precaution, move to a place of safety?

　　就算僅僅是為了以防萬一，難道他就不能挪到安全的地方嗎？

　　I took the precaution of clearing out my desk before I left.

　　我臨走時特地事先把辦公桌清理了一下。

　　As a precaution against earthquakes, the building is being reinforced.

　　為了防震，這座樓正在加固。