问题补充：
The subway in our city, and I’m sure there will be fewer traffic jams in the future.
A. is building
B. is built
C. is being built
D. will build
答案：
A. is building
B. is built
(答案→)C. is being built
D. will build
解析：这里地铁是被建设的对象，应用被动语态，根据下文可知句子为进行时态才符合题意，故选C，我们城里正在建地铁，我相信将来交通堵塞回变得更少。
