三者表示的意義差不多,都表完成意義．
以下為本人認為的細微差別．
already 表”已經(jīng)”,一般用在助動詞后,行為動詞前．
e.g.They have already left their motherland.
他們已經(jīng)離開了祖國．
just表”剛剛”,一般也用在助動詞后,行為動詞前．
e.g.They have just left their motherland.
他們剛離開他們的祖國．
yet表”已經(jīng)”,用在否定句中,一般在句末,有時用于助動詞后．
e.g.They haven't left their motherland yet.
or They haven't yet left their motherland.
他們還未離開他們的祖國