问题
选择题
He had to pause from time to time to wipe the sweat from his forehead, because the air-conditioning system _________.
A．broke in
B．broke up
C．broke out
D．broke down
答案
答案：D
题目分析：A. broke in闯入，插话，B. broke up 分手，解体，C. broke out 爆发，D. broke down崩溃，破裂，出故障，句意：他不时的停顿擦前额的汗，因为空调系统出故障了。所以选D。