问题补充：
In order to make Chongqing more beautiful, lots of trees on both sides of the street.
A. should build
B. have built
C. must be built
D. will build
答案：
A. should build
B. have built
(答案→)C. must be built
D. will build
解析：本题需要的是被动语态，主语是被发生的，是动作的承受者，只有C为被动语态结构，其余的选项，都是主动语态，故选C
