举例说明吧...yet:还...I haven't read it yet;
while:1,当...时,2.表示对比的...he is playing ,while I am reading.
however和but的区别：But 在文法上是一个连接词,即用来连接两句完整句子的字；但 however 只是个adverb,不能用来连接句子.而用 however 时要用 comma 把它从句子其他部份分开.简单例子：
I love her, but she doesn't love me.
如果换上 however 就错了文法.要开新句才可用 however：
I love her. However, she doesn't love me.
However 可用於句子中间,用作加强语气的 interruption.其实这才是 however 最好用的地方.英文写作专家 William Strunk 在其巨著 "The Elements of Styles" 写道：永远不要把 however 放在句子开头 (however 另外一个用法除外).