1. 用于序數(shù)詞前：用在序數(shù)詞前表示“再一”“又一”。如：

She thanked him a second time.

她再次向他道謝。

Shall I ask her a third time?

我還要問她一次嗎?

2. 用于由動詞轉(zhuǎn)化來的名詞前：表示一次、一番等義(通常與 have, take, make, give 等動詞連用)。如：

We’ve already had a try at it.

我們已經(jīng)試過一下。

I went down to the beach and took a swim.

我到海邊去游了游泳。

3. 用于專有名詞前：相當于a certain，意為“一個”“某個”。如：

The house next door has been bought by a Mr Jones.

隔壁的房子被一個叫瓊斯的先生的人買下了。

4. 用于抽象名詞前：使之具體化，表示與該之相關(guān)的具體的人或事。如：

He was a success in business.

他事業(yè)成功。

It’s a pleasure to talk with you.

同你談話是件令人愉快的事。