雅思写作高分精华——时态转换

学英语的时候常听老师说，句子有从句的话，从句的时态变化应该跟随主句的时态变化。

比如 I tell him that I have finished my homework. 我告诉他我已经写完作业了

I told him that I had finished my homework. 我告诉了他我那时就已经写完作业了

这条金规玉律我沿用了很久。然而随着英语使用的增加，

我发现英语的时态更多地是作为某种语气来使用，而不是一成不变的语法。

因此时态的运用也应该是灵活的，要根据想要表达的内容而变化，而不是简单地从句跟随主句。以下，我用三个例子来说明：

他发现, 要把茶叶里所有有用物质都提取出来，就必须把茶叶在80度的温度下发酵20分钟。

He discovered that in order to extract all the good compounds, you had to brew tea for twenty minutes at 80 degrees.

He discovered that in order to extract all the good compounds, you have to brew tea for twenty minutes at 80 degrees.

主句discover是过去时，如果按照习惯用法，从句也应该二话不说地使用一致的时态。可这里句子所表达的是这个人发现了一条客观规律，虽然他是过去发现的，但这条规律是直到现在还是通用的。因此这里应该用 have to 而不是 had to。

对于（问卷里的）每一个区域，受访者都被要求作答自身的知识水平是否足够或者是否需要提高。

For each area, they were then asked to indicate whether they believed their level of knowledge was adequate or requires improvement.

For each area, they were then asked to indicate whether they believe their level of knowledge was adequate or requires improvement.

这则问卷调查的是受访者对问卷题目的一个即时反应，也就是说访者当下的思考状态。也因此这里更为准确的表达应该是 believe 而不是 believed.

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