在检查电灯不亮的原因时，将灯头盖打开，用测电笔分别接触灯头的两接线柱，氖管都亮，可能的故障原因是 [ ]

A.灯丝断了

B.零线断了

C.火线断了

D.火线和零线直接接通了

Not until _____ his shoes did he enter one of the rooms of the Japanese house.

A．he removes

B．did he remove

C．he had removed

D．had he removed