问题补充：
Lots of trees in our city over the years. It is becoming greener and greener!
A. are planting
B. have planted
C. will be planted
D. have been planted
答案：
A. are planting
B. have planted
C. will be planted
(答案→)D. have been planted
解析：根据over the years 表示在过的几年里，一般与现在完成时态连用，又因为主语为物，是动作的承受者，故要用被动语态，故选D
