问题
选择题
Tens of thousands of people have visited Expo 2010 Shanghai China ________ it opened in April. [ ]
A. for
B. before
C. since
D. while
答案
答案：C
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Tens of thousands of people have visited Expo 2010 Shanghai China ________ it opened in April. [ ]
A. for
B. before
C. since
D. while
答案：C