— Must I return the book by the end of next month? 

—           . You can keep it as long as you like. [ ]

A. No, you mustn't

B. No, you can't

C. Yes, you have to

D. No, you needn't

为节约用水，某市决定用水收费实行超额超收，标准用水量以内每吨2.5元，超过标准的部分加倍收费。某用户某月用水15吨，交水费62.5元，若该用户下个月用水12吨，则应交水费多少钱？（）

A.42.5元

B.47.5元

C.50元

D.55元