问题补充:
It was from May 1 to October 31,the World Expo Shanghai will be held, is a great event for the Chinese people.
A. when; that
B. that; when
C. which; when
D. that; which
答案:
A. when; that
B. that; when
C. which; when
(答案→)D. that; which
解析:第一空that构成强调句型;第二空which引导非限制性定语从句,并充当其主语。