问题
选择题
They did everything in their power to save the building dating back to the Qing Dynasty, but their efforts were _______.
A．in turn
B．in time
C．in vain
D．in need
答案
答案：C
题目分析:句意：他们在能力范围内尽一切努力去挽救始于清朝时期的建筑，但是他们的努力是徒劳的。A轮流；B及时；C徒劳；D需要。根据but可知后面和前面内容是转折关系，选C。