Mary went to the box office at lunch time, but all the tickets ____out.
Not only _____ polluted, but _____ crowded.
A middle-aged woman came _____ to the bus stop only_____ the bus had gone.
Only _____ as an interpreter _____ how important it was to practise speaking English.
Only when _____ possible to settle the problem.
The boy said ___ couldn't he work out the problem but his teacher didn't know how to do it.