— Dorothy, would you like to join me in an outing?

— _____, but I am working on my paper all weekend.  [ ] 

A. Thanks      

B. All right        

C. It's OK        

D. Not at all

下面关于空气污染指数的叙述中错误的是[ ]

A．污染指数大，空气清新，对人体健康有利

B．污染指数大，空气污浊，对人体健康有害

C．污染指数越小，空气质量状况越优      

D．污染指数越大，空气污染越严重