請問already/yet/just呢三個字應該幾時用?

already-I have already did my homework(已經)
just-I have just finished my homework(剛剛)
yet-I have not finish my homework yet(還 )

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.

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mwl r c hing, 我覺得001 的第一答案應寫作 I have already done my homework 應該用 done 唔係用 did.

2010-11-27 15:06:10 補充：
1. I have already done my homework.
2. I have just finished my homework.
3. I have not finished my homework yet.

001的1,2 答案不錯, 但 第3句 應寫作 I have not yet finished my homework.或
I have not finished my homework yet.