问题补充：
people are concerned about now is the Shanghai World Expo, which start on May 1st.
A. What; is due to
B. Which; is going to
C. That; is to
D. What; is about to
答案：
(答案→)A. What; is due to
B. Which; is going to
C. That; is to
D. What; is about to
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