单选题 If a guest wants to tip the housekeeping staff, it's best to leave a little something in an envelope each night instead of a larger amount ______ checkout.
A. due to B. owingto C. prior to D. as to

【正确答案】 C

【答案解析】[解析] 根据句中“退房之前”可知，只有C项符合题意。priorto意为“在……之前，居先”。根据题意可知，C项为正确答案。