“yet”用于否定句.放在句末
如：
I have not finished reading the book yet.
“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)