From time to time, some parents asked themselves the question ______ what they had done for their kids was worth doing.
No matter how frequently _____ the works of Beethoven always attract a large number of people.
I heard that you really had a wonderful time at John's birthday party, _____?
Modern science and technology has _____ communication between people far apart.
Under no circumstance _____ to tell lies to parents.
The professor said he could talk on _____ interested the audience.