The central heating system of this office building is down and several workers it right now.
A. had repaired
B. have repaired
C. repaired
Dare repairing
网友回答
A. had repaired
B. have repaired
C. repaired
(答案→)D. are repairing
解析：句意：这座办公楼的集中供暖系统坏了，几名工人目前正在修理。表示现在正在做某事，用现在进行时，选D。