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。