It was three years since they worked here.这是高二的一道改错题，答案是把worked 改成 had worked

这个答案对吗？

答案绝对正确
如果从句用过去时
主句应该是一般现在时或现在完成时
It is/has been three years since they worked here.
It was three years since they had worked here.

不对。since后面要接一般过去式。since之前用完成时。可以改成：it has been 3 years since they worked here。

对的。since 引导的时间状语从句表示“自从。。。以来”，其用法主要有两种。 1. It be +表一段时间的词语+since引导的时间状语从句。 e.g. It was three years since we had been there. 我们在那呆过三年。 2. 现在完成时主句+since引导的一般过去时的时间状语 e.g. he hasn't been home since he graduated. 在这道题中，是第一种情况。

Since在特殊句型中的应用 句型I：“It is （has been）+时间+since+持续性动词的过去时”，表示“自从……以来到现在已有多久。”例如： It has been quite some time since I was last in London.我上次离开伦敦至今颇有一段时间了。 句型II：“It was+时间+since+持续性动词的过去完成时”,表示“从……到过去某时间点以来”，例如：It was three years since we had been here.那时我们在这已呆了三年。 所以该题可以有两种改法： 一是把was换为is或has been 二是把worked改成 had worked 希望帮助到你

答：这一题句很麻烦，不好改！ 首先，since sth. happened 自从某事发生以来（从句为短暂性动词），主句多用“现在完成时”，表示自某事（过去）发生以来，到现在为止，时间已经过去多久了，本来的句型是： It has been some time since sth. happened. 如果是间接引语，或者以过去的另一时间作参照，since从句还是用一般过去时态，主句用过去完成时态： He said that it had been some time since sth. happened. 我们又知道，现代英语中，第一个句型可以用is代替has been: It is some time since sth. happened. 表示：自从某件事情发生以来（到现在为止），时间已经过去多久了。 除非有上下文，除非有过去的另一时间作参照，过去完成时不出现在单句中，所以，除了： He said that it was some time since sth. happend. 外，单句不出现过去完成时的句子： X It had been some time since sth. happened. (自从某件事情发生以来，到过去何时为止？已经有一段时间了） 同理也不单独出现下面的句子： X It was some time since sth. happened。 即使从句用过去完成时，也没有道理： X It was some time since sth. had happened. 这个从句的过去完成时，其过去的参照时间是哪一个？是在那个过去时间之前发生的？不要说是主句状态was之前发生的吧？ 因为本来就是：It has been some time since sth. happened. 如果将其变为间接引语，从句是不需要用过去完成时态，而是主句用： He said it had been some time since sth. happened.(自从过去那件事情发生以来，到说话时为止）。 另外，此题句还在since 从句中出现了“延续动词”，使得问题变得更加复杂化。 有人认为：如果是从句的谓语动词是延续性动词，则主句的状态（或延续动作的）起点时间从从句动作结束时算起，翻译时用否定句。举例说明： It is(=has been) 10 years since he left Shanghai. 译：自从也离开上海以来（至今）已有10年了