soon

这两个词(组)的区别是:soon表示“不久”“很快”,强调时间很短; at once表示“马上”“立刻”,强调动作随即发生。例如:

He soon became active in the class.他在班上很快就变得活跃起来。

When I heard the knock,I opened the door of the room at once.我听到敲门声马上就把房门打开了。

这三个短语都可表示“一…就…”。它们的区别是：

1.as soon as可转化为no sooner...than或hardly...when结构。例如:

As soon as I heard the knock I opened the door.

No sooner had I heard the knock than I opened the door.

Hardly had I heard the knock when I opened the door.

当我听到敲门声,我马上就开门了。

2.as soon as通常用于一般时态, no hardly...than和hardly...when通常用于过去完成时。例如:

As soon as you finish your job, let me know.你一完成工作就告诉我一声。

No sooner had the doctor arrived than he began treating the sick.医生一到马上就抢救病人。

I had hardly started when it began to rain.我刚动身就下起雨来了。

这三个词都可表示“很快”。它们的区别是：

soon强调的是预期的时刻不久就会到来, fast和quickly强调的是动作进行的速度快。例如:

Their population is growing fast.他们的人口增长得很快。

Come quickly, he's drowning!快来,他溺水了。