Beijing is one of the in the world today.A. busiest cityB. busiest citiesC. busy cityD. b

问题补充：

Beijing is one of the in the world today.

A. busiest city

B. busiest cities

C. busy city

D. busy cities

答案：

A. busiest city

(答案→)B. busiest cities

C. busy city

D. busy cities

解析：本题主要考查的一是busy的最高级为busiest，二是one of the+名词复数形式，故选B