1) but表示转折，while表示对比。
Some people love cats,while others hate them.
典型例题
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与前面形成转折，符合语意。而表并列的and， 结果的so，原因的as都不符合句意。
2)not…but…意思为"不是……而是……"
not 和but 后面的用词要遵循一致原则。
They were not the bones of an animal,but (the bones) of a human being.