The World Expo is being held at a time the world is looking for a new kind of balance

问题补充：

The World Expo is being held at a time the world is looking for a new kind of balance between nature and cities．

A. when

B. where

C. which

D. that

答案：

(答案→)A. when

B. where

C. which

D. that

解析：考查定语从句的关系词。此处time作先行词，其在定语从句中作时间状语。句意：世博会在一个世界正在寻找新的自然和城市的平衡的时代举行。