It+be+时间+before/since/when/that 句型辨析

I. since  

1.It is/has been+时间段+since sb did sth某个动作发生持续多久

eg:It is/has been three years since he finished the work.

自从他完成这项工作已经三年了.

2.该句型中若since后跟延续性动词，要翻译成否定含义,即“没做某事已经多久了”.

eg:It has been three years since he worked here.他不在这工作已经三年了.

It has been three years since he smoked.他已经戒烟三年了.
但是：It has been three years since he began to smoke.
      他吸烟有三年了。

II.before.

1.It was/will be+时间段+before... 过多长时间将发生某动作或事情；或过了多久发生了某事或动作。

eg:It was three years before he finished the work.他花了三年才完成这项工作.

It will be three years before he finishes the work.他得花三年才能完成这项工作.

2.It won't be/take long before...不久就会…

eg:It won't be long before he finishes the work.他不久就会完成这项工作.

 IIIwhen.

when没有固定与It is…连用的句型.when可表示时间点或时间段，因此从句中短暂性动词或延续性动词均可用.when还可作并列连词，表示突然发生一个动作,等于and at that time.常用句型:

1主语+was/were doing when...

2主语+was/were about to do when...

 It+be+时间+before/since/when/that重要考点练习

It +be+时间+before/since/when/that…是高考中每年必考的重要考点，而学生却对这个句型中几个关联词的选择把握不准，造成失分。我在试题讲解的过程中设计了以下几个小题，让学生去分析，整理，归纳，效果很好。

    1. It was two years ________he realized the truth.

    2. It will be two years ________ the economic situation improves.

    3. It was two years later ________ he realized the truth.

    4. It is /has been two years ________ he lived here.

    5. It was midnight ________ he arrived home.

    6. It was at midnight ________ he arrived home.

    7. It was not until midnight _______ he arrived home.

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

    「答案与解析」

    1、2两个小题都选A. 第一题意为：两年后他才得知真相。第二题意为：经济形式要等两年后才会有所好转。

    「归纳」It was/ will be +一段时间+before+句子是高考一个重要考点。意为：多久之后才……

    要注意：It will be +一段时间+before+句子，before引导的是一个时间状语从句，所以后面的从句要用一般现在时态表将来。

    3. D 此题为强调句型。把It was…that去掉后，句子仍然成立：He realized the truth two years later.

    4. C 本句意为：他不住在这儿已经两年了。

    「归纳」为since意为自从某时或某事发生以来，故since后从句时，从句的时态应用一般过去时态，而主句应用现在完成时态。如表示某某事发生多久了，则用：It is/ has been+一段时间+since+从句。

    「注意」It is/ has been+一段时间+since+从句。在本结构中，从句的谓语动词如为延续性动词时，翻译时要从动作结束时算起。

    5. B本句为定语从句，先行词为midnight，在从句中作状语。要注意与第6小题的区别，第6题为强调句型，故答案应为that.

    6.D 再看下面两题：

    （1） It was the park ________ he first met his wife.

    （2） It was in this park ________ he first met his wife.第一题答案应为where，为定语从句；第二题答案为that,为强调句型。

    7.D本题亦为强调句型结构：It was not until…that…意为：直到……才……