yet, already 辨析

Yet(adv.)---"已经".与Already一样均用于谈论某一特定时间之前可能完成的某项动作.
Yet只用于否定句和疑问句中.
Already(adv.)---"已经".常用于肯定的陈述句中,也可用于疑问句以表示惊奇.

例:Has the bell rung yet? --- It has not rung yet.
已经敲钟了吗? --- 还没有.
I've started learning Greek, but I haven't got very far yet.
我已经开始学习希腊语,但只是刚刚入门.
John hasn't done much work yet, but Anne has already finished.
约翰还没做多少工作,可是安妮已经做完了.
Have you finished lunch already? It's only 12 o'clock.
你已经吃过午饭了吗? 刚刚12点.