(1)but用作并列连词，常用来连接两个并列的句子或一个句子中的两个并列成分，表示强烈的对比、转折，两个并列成分之间可以用逗号隔开，也可以不用，但是but不能置于句首，并且后面不用逗号隔开。

　　They rushed to the station but the train had left.

　　他们匆忙赶到车站，但是火车已经开走了。

　　It is cold in winter here, but it is not hot in summer.

　　这里冬天很冷，但是夏天不热。

　　[名师点津]　but 作连词还可用于"I'm sorry/ Excuse me, but ..."句式中表示歉意，but本身没有意义。

　　I'm sorry, but I can't help you with the problem.

　　很抱歉，我不能帮你解决这个问题。

　　(2)however用作副词时，意为"然而；但是"，用以引出令人吃惊或表示对比的话语，可以放在句首、句中或句末，但通常有逗号与主句隔开。

　　You may be right. However, I still want to do what I planned.

　　你可能是正确的。但是，我仍然想做我计划好的事情。

　　Your answer is wrong, however.

　　不过你的答案是错的。

　　He hasn't arrived. He may, however, come later.

　　他还未到，不过，他可能晚一会儿来。

　　[名师点津]　however还可以用作连接副词，意为"无论如何，不管怎样"，后面常接形容词或副词，引导让步状语从句，该从句可放在主句之前或之后。

　　You should try to get a good night's sleep, however much work you have to do.

　　不管你有多少工作要做，你都应该好好休息一个晚上。

　　He tried his best to solve the problem, however difficult it was.

　　他尽力解决这个问题，不管它有多困难。

　　[即时演练1]

　　(1)选词填空：but, however

　　①He is young but very experienced.

　　②However long it takes, I'm going to get the job finished.

　　③Later, however,_he changed his mind.

　　④He has three daughters but no sons.

　　⑤You should always try to achieve more, however well you have done before.

　　(2)完成句子

①He likes sports, but_his_wife_likes_music.