Beijing is the capital of China and it is one of cities in the world. A. bigB. biggerC. b

问题补充：

Beijing is the capital of China and it 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：北京是中国的首都，它是世界上最大的城市之一。One of +the+形容词最高级+复数名词，表示最……之一。选D。