It was from May 1 to October 31 the World Expo Shanghai will be held is a great

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。