— What's the noise? It sounds as if it comes from upstairs.

— _____. It must be the window-cleaner working, next door. [ ]

A. I'm not sure

B. I hope not

C. I'd rather not

D. I don't think so

甲、乙、丙三家超市为了促销一种定价为m元的商品，甲超市连续两次降价20%；乙超市一次性降价40%；丙超市第一次降价30%，第二次降价10%，此时顾客要购买这种商品，最划算的超市是         .