already和yet的用法区别是什么

现在完成时中,already和yet都可以表示“已经”的意思.
两者区别主要如下：
already用于肯定句,放在句中或句尾.
如：I've already been there twice.
= I've been there twice already.
我已经去过那里两次了.
yet用于否定句或疑问句中,放在句尾.
如：I haven't finished reading the book yet.
我还没有读完那本书.
Have the children come back home yet?
孩子们回家了吗?