He had to pause from time to time to wipe the sweat from his forehead because the air-con

问题补充：

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：

A. broke in

B. broke up

C. broke out

(答案→)D. broke down

解析：考查动词短语辨析。break in打断； 闯入； 开始工作；break up结束，散开；分解；break out爆发；break down崩溃，垮掉；出毛病；抛锚。题干意思是：他时不时地停下来擦去额头的汗水，因为空掉出毛病了。选D。