We in this pool when we were young, but now it fish.
A. are used to swim; used to keep
B. are used to swimming; used to keep
C. used to swimming; is used to keep
D. used to swim; is used for keeping
网友回答
A. are used to swim; used to keep
B. are used to swimming; used to keep
C. used to swimming; is used to keep
(答案→)D. used to swim; is used for keeping
解析：be used for sth被用于某事;used to do sth过去常常做某事.句意：当我小的时候，我常常在这个池子里游泳，但是现在它被用来养鱼。