The city of Qingdao has been working on building itself up as a city of sails it successf

问题补充：

The city of Qingdao has been working on building itself up as a city of sails it successfully hosted the Olympics’ sailing program.

A. after

B. since

C. when

D. until

答案：

A. after

(答案→)B. since

C. when

D. until

解析：考查连词。题意：自成功举办08奥运游泳项目以来，青岛一直致力于建设航海城。现在完成进行时has been working提示用since引导状语从句。故B项正确。