问题补充：
The Nile River flood large areas but now the water produce electricity.
A. used to; is used to
B. used to; used to
C. was used to; is used to
D. was used to; used to
答案：
(答案→)A. used to; is used to
B. used to; used to
C. was used to; is used to
D. was used to; used to
解析：考查固定句型。句义：尼罗河过去常常淹没大片地区但是现在被用来发电。固定句型used to do 过去常常（而现在不。。。） be used to do 被用来。。。，根据句意所以A正确。
