事先

In a sentence

• 我们应该事先做好安排，以避免意外情况。

  We should make arrangements beforehand to avoid unexpected situations.

  In this sentence, '事先' is used as an adverb indicating an action taken earlier before the main event happens.

• 事先的准备工作是成功的关键。

  The preliminary preparation is the key to success.

  Here, '事先' functions as a modifier for '的准备工作,' describing that the preparations were done prior to the event.

• 他事先没有通知我们，所以我们措手不及。

  He did not notify us in advance, so we were caught off guard.

  In this example, '事先' serves as an adverb modifying '没有通知,' showing that the notification was expected to happen earlier but did not.