trees have been planted these years.A. MillionB. MillionsC. Million ofD. Millions of

问题补充：

trees have been planted these years.

A. Million

B. Millions

C. Million of

D. Millions of

答案：

A. Million

B. Millions

C. Million of

(答案→)D. Millions of

解析：

这题考查数词的用法，因为这句话没有具体数字，所以不能选A，Millions of是“上百万的”，修饰trees，句意是：这些年种了上百万的树。选D。