) but表示轉折，while表示對比。
　　 some people love cats, while others hate them.

典型例題　
--- would you like to come to dinner tonight?　　
--- i'd like to, ___ i'm too busy.
　a. and　 b. so　 c. as　 d. but　　
　答案d。but與前面形成轉折，符合語意。而表并列的and， 結果的so，原因的as都不符合句意。

　2) not…but… 意思為"不是……而是……"
　　 not 和but 后面的用詞要遵循一致原則。
　　 they were not the bones of an animal, but (the bones) of a human being.