still 能不能放句尾？？

“already”， “yet”和“still”有什么区别？
what's the difference between "already", "yet" and "still"? 

answer: "already" is used in affirmative sentences; "yet" is used in negative sentences.
e.g. 
1) he has already finished his homework.
2) i have not finished reading the book yet. 
note: when "already" is used in an interrogative sentence, it expresses a surprise.
e.g. have you already seen him? 
"still" can be used in both affirmative and negative sentences. it expresses the meaning of continuation of actions and states of affairs.
e.g. 
1) she still likes him.
2) i still can not understand you. 
note: the position of "still" before or after the verb makes difference in meaning.
e.g. 
1) he is still standing. (continue to stand)
2) he is standing still. (=standing motionless) 

“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)