When we arrived in used to be called the foggy capital we found London completely changed

问题补充：

When we arrived in used to be called the foggy capital，we found London completely changed.London is now one of the capital cities in the world with the finest air quality.

A. which

B. what

C. that

D. where

答案：

A. which

(答案→)B. what

C. that

D. where

解析：宾语从句中缺少主语，故用what连接。