Mr Dong ______live in the old Walled City . So he knows it very well.
A. used to B. is used to C. has used to D. used as
【答案】A
【解析】句意：董先生过去常常住在古老的 Walled城市，因此他非常熟悉那里。used to do sth 过去常常做某事，be used to do sth被用来做某事；过去常常做某事，用过去时态，C是现在完成时态结构，所以不对，D used as用作，通常是be used as把---当作---用；根据句意故选A