Already,yet,just用於present perfect tense(PP tense)
Already(已經)用在PP tense中間或PP tense後面_I've already done the homework.I've done the homework already.
Just(剛剛)用在PP tense中間_I've just eatten the fish.
Yet(還)用在問題_Have you done the homework yet?
2010-11-30 19:41:34 補充:
Yet(還)用在回答(不)I haven't done the homework yet.