_________ happened to be no one in the building when the fire broke out.
What do you think should _____ the shopping list?
The last factory ______ I am going to visit is the place _____ my mother worked five years ago.
The dog, if trained ____, will be made a good watch-dog one day.
The one and only thing I ____ is whether you take a good rest!
-He asked Tom, “Have you finished your homework?” -He asked Tom .