—Tom came to work last Friday ,but no one has seen him since. — he have had an accident ?
The hungry man eats his food _______he hadn ' t eaten for a week.
We must ________ our task, however hard it is.
________ the same mistake again made his parents very angry.
The police are________to conclude that the cause of fire had been a cigarette end.
I don‘ t know how to use a computer,_________.