问题
选择题
The World Expo 2010 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
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：2010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。