yet与stilll的不同

“already”用于肯定句，“yet”用于否定句。
如：
1) He has already finished his homework.
2) I have not finished reading the book yet.
注意：“already”用于疑问句时，表示惊奇。
如：Have you already seen him?
“still”既可用于肯定句又可用于否定句，表示动作或状态的持续。
如：
1) She still likes him.
2) I still can not understand you.
注意：“still”置于动词前后，会使句意发生变化。
如：
1) He is still standing. (continue to stand)
2) He is standing still. (=standing motionless)

YET是“至今” 多与完成时连用

still是“直到，截止到“