ever
ever 和 never 表达的是过去一个不明确时间的概念（例如：Have you ever visited Berlin?）ever 和 never 一律放在主要动词（过去分词）前。ever 是用在：
问句中
举例
Have you ever been to England?
Has she ever met the Prime Minister?
在否定句
举例
Haven't they ever been to Europe?
Haven't you ever eaten Chinese food?
用 nothing + ever 或 nobody + ever 形式的否定句
举例
Nobody has ever said that to me before.
Nothing like this has ever happened to us.
带有「the first time」的句子
举例
It's the first time that I've ever eaten snails.
This is the first time I've ever been to England.
never
「never」意指「过去一次也没有」，跟「not ..... ever」的意思是一样的。（例如：I have never visited Berlin.）
I haven't never been to Italy.
I have never been to Italy.
already
「already」意指某个动作已经发生在过去一个不明确的时间，传达「无需再重复」的意思。
举例
I've already drunk three coffees this morning. (= 而且你还又给我一杯！）
Don't write to John, I've already done it.
这个字也会用在问句中：
Has she finished her homework already?
「already」可以放在主要动词（过去分词）前，或放在句尾：
I have been to Tokyo already.
yet
「yet」用于否定句和问句，一般会放在句尾；意指在过去和现在的一段时间内曾经有（或从未），直到现在曾有（或未曾），以及包括现在有（或没有）。
举例
Have you met Judy yet?
I haven't visited the Tate Gallery yet
Has he arrived yet?
They haven't eaten yet