1. If 引导的条件句---第一条件句

形式：

If I am better tomorrow, I will get up.

If I have a headache, I will take an aspirin.

If she finishes early, she will go home.

用法：

第一类条件句从句中的动词用一般现在时，主句中的动词用will/shall 动词原形。用来表示询问或谈论十分可能的事情。如果我们认为将来的事件可能会发生，就可以用第一条件句去描述将会发生什么事或不会发生什么事。

2. 过去进行时

形式：

过去进行时由was/were -ing 分词构成。

I was writing.

We were writing.

用法：

①表示过去某时正在进行的动作。

What were you doing last night at seven o’clock?

Workers were building a dam last summer.

②与always 连用表示过去经常重复的动作。

He was always changing his mind.

She was always coming back late.

3. 现在完成时

形式：

现在完成时是have/has ed分词构成的。

I have (I’ve) played.

He has (He’s) worked.

用法：

①表示动作或过程发生在说话之前某个没有明确说出的过去时间，现在已经完成了，并与现在的情况有联系。

现在完成时可以不带时间状语。

She’s turned off the light.(灯在一个过去时间被关了，说话时刻仍然关着。)

现在完成时可以表示最近发生的动作。

She’s already gone.

It’s rained quite recently.

现在完成时可以表示反复性和习惯性动作。

We have often been there.

I’ve seen the film three times a month.

②表示开始于过去并持续到现在(也许还会持续下去)的动作。

现在完成时和“直到现在”的状语连用。

Up till now we have planted over 24,000 fruit trees.

So far everything has been successful.

现在完成时与since 和 for 连用。

I’ve known him since 1950.

I haven’t smoked a cigarette for a year