I’m very proud of that Beijing is one of cities in the world.A. bigB. biggerC. biggestD.

问题补充：

I’m very proud of that Beijing is one of cities in the world.

A. big

B. bigger

C. biggest

D. the biggest

答案：

A. big

B. bigger

C. biggest

(答案→)D. the biggest

解析：句意：北京是世界最大的城市之一，我感到非常自豪。one of+形容词的最高级形式，表示“最…之一”，形容词的最高级前面加the,故选D