請注意以下三個句式的區別和意思上的差異（其中的 is 根據情況可以有其他時態形式）：

It is + 時間段 + since… 的意思是“自從……以來有一段時間了”。

It is + 時間點 + when… 的意思是“當……的時候時間是……”。

It is + 時間段 + before… 的意思是“在……之前有一段時間”。

請看以下用例：

It’s ten years since they got married. 他們結婚到現在已經十年了。

It was past one o’clock when he came in. 他回來時已經一點多了。

It won’t be long before they understand each other. 過不了多久他們就會互相了解的。

有時翻譯可以比較靈活：

It’s a long time since I met you last. 好久不見了。(直譯：自上次見到你以來有很長一段時間了。)

It’s about three years since I last played basketball. 我差不多有三年沒有打籃球了。(直譯：自從我上次打籃球以來已差不多有三年了。)

請看有關高考題(答案為DDBCDC)：

1. That was really a splendid evening. It’s years ______ I enjoyed myself so much. (安徽卷)

A. when       B. that         C. before      D. since

2. It was some time _____we realized the truth. (山東卷)

A. when                B. until                   C. since                 D. before

3. —Did Jack come back early last night?

—Yes. It was not yet eight o’clock _____he arrived home. (福建卷)

A. before              B. when                 C. that                    D. until

4. Scientists say it may be five or six years _____it is possible to test this medicine on human patients. (福建卷)

A. since                 B. after                   C. before               D. when

5. It was evening       we reached the little town of Winchester. (天津卷)

A. that                    B. until                   C. since                 D. before

6. It ______ long before we ______ the result of the experiment. (上海春)

A. will not be; will know                    B. is; will know

C. will not be; know                           D. is; know

【模擬訓練】

1. It was about midnight ______ we found the lost child, crying under a tree.

A. that                    B. until                   C. when                D. where

2. It's some time ______ I have spoken to you about this matter.

A. that                   B. unless               C. since                 D. until

3. It was ten ______ he stood at aunt’s door and rang the bell.

A. when                B. until                   C. since                 D. that

4. I think it won’t be long ______ they understand each other.

A. when                B. until                   C. since                 D. before

5. How pleased I am tonight! It’s years ______ we had so great a time together.

A. when                B. that                    C. before               D. since

6. It was some time ______ we realized how important the matter is.

A. when                B. until                   C. since                 D. before

7. —Did you come home very late last night?(www.hz123456.com)

—No. It was just half past seven ______ I appeared before my parents.

A. that                   B. when                 C. until                   D. since

8. How time files! It seems like years ______ I last saw you.

A. when                B. that                    C. since                 D. before

9. It’s more than half a century ______ the People’s Republic of China was liberated.

A. when                B. that                    C. since                 D. after

答案：1—5 CCADD  6—9 DBCC