On April 24 Tsinghua University its 100th anniversary at the Great Hall of the People in

问题补充：

On April 24, Tsinghua University its 100th anniversary at the Great Hall of the People in Beijing.

A. congratulated

B. challenged

C. celebrated

D. participated

答案：

A. congratulated

B. challenged

(答案→)C. celebrated

D. participated

解析：四个选项分别表示向某人祝贺、挑战、庆祝（大型活动）和参加（某事），根据题意选C，四月二十四日，清华大学在北京人民大会堂庆祝了它的100周年纪念日。