ad.  事先，预先，事前

• By storing enough food beforehand.

  提前储存食物

• These stages can be studied, and strategies to be used in each can be planned beforehand. 提前计划

• When you give a speech, it’s natural to feel nervous beforehand.

  你在演讲之前感到紧张是很自然的。

• I wish we'd known about it beforehand.

  要是我们预先知道这事就好了。