问题
选择题
The central heating system of this office building is down and several workers ______ it right now.
A．had repaired
B．have repaired
C．repaired
D． are repairing
答案
答案：D
题目分析：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。