Many years had ______ before they returned to their original urban areas.

A．to stay
B．is to stay
C．to stay at
D．is for staying

A．Farrell was injured because he negligently ran his engine off the track.
B．Farrell would not have been injured if the switchman had been more careful.
C．The court argued that the victim had accepted the risk since he had willingly taken his job.
D．The court decided that the railroad should not be held responsible.