四、一般现在时的用法
1. 主要表示目前的特征或状态、现在经常性或习惯性的动作、客观存在及普遍真理等。如：
I know you are busy. 我知道你很忙。
She visits her parents every day. 她每天去看她的父母。
Summer follows spring. 春天之后是夏天。
2. 在状语从句中一般现在时可表示将来。如：
Turn off the lights before you leave. 走前关灯。
I’ll give her the telex when she comes. 她来时把电传交给她。
五、过去进行时的用法
1. 表示在过去某一时刻或某一阶段正在发生的动作。如：
I was having a shower at that time. 那时我正冲澡。
2. 表示某个短暂性动作发生的背景。如：
I was reading the newspaper when the doorbell rang. 我正在看报，突然门铃响了。
3. 过去进行时在语境中的运用。如：
I waved to her but she wasn’t looking. 我向她挥手但她没往这边瞧。
She didn’t hear the doorbell. She was listening to the radio. 她没听见门铃响，她在听收音机。
注：与always, forever, frequently等副词连用，可表示某种感情色彩。如：
She was forever complaining. 她老是抱怨。(厌烦)
She was always thinking of others. 她老是想到别人。(赞扬)
六、过去完成时的用法
1. 表示在过去某一时刻或某一动作之前已经完成了的动作(即所谓的“过去的过去”)或表示从过去某一时刻开始一直延续到另一过去时刻的动作或状态。如：
When we arrived he had already left. 我们到达时他已经离开了。
By six o’clock he had worked twelve hours. 到6点钟时他就已工作了12小时。
2. 表示未曾实现的希望或打算，主要用于 hope, want, expect, think, suppose, plan, mean, intend 等动词。如：
I had meant to come, but something happened. 我本想来，但有事就没有来。
We had thought to return early but they wouldn’t let us go. 我们本想早回来的，但他们不让我们走。
3. 用于某些特殊句型。如：
This was the first time he had ever been late. 这是他第一次迟到。(类似 it was the first time that…后的从句谓语要用过去完成时)
It was three years since we had left the city. (那时)我们离开那座城市已有三年。(类似 it was…since…后的从句谓语要用过去完成时)
We had no sooner set out than a thunderstorm broke. 我们刚出发就遇到了大雷雨。(no sooner…than 的主句谓语要用过去完成时)
He had hardly arrived when it began to snow. 他一到，天就下起雪来了。(hardly…when 的主句谓语要用过去完成时)