yet still already 这三个词经常放一块来区分:
Yet is used to say that something has not happened or a situation has not started to exist, or to ask if something has happened
• It isn't time to go yet.
• Have you seen him yet?
Still is used to say that an earlier situation has not changed
• My parents were still asleep (NOT yet asleep).
• I still don't understand.
Already is used to emphasize that something has happened or a situation has started to exist
• He had already published two novels.
• They already knew one another.
It is also used in questions to show surprise that something has happened sooner than expected
• Have you been there already?
参考资料:朗文当代英语词典