How much are they? Five yuan for one

A. every     B. once     C. each   D. for every

— How much are these socks?
—______ two dollars.

— How much are the two pairs of trousers?
— They are not expensive. I think one hundred dollars ______ enough.

— How much are the two pairs of trousers?

— They are not expensive. I think one hundred dollars ______ enough.

A．is                B．are              C．were             D．was