—How much if I wan to take one?—You can take as many as you like because they are free of _____.
Bicycling is good exercise; ____, it does not pollute the air.
Mary is really good at taking notes in class. She can almost every word her teacher says.
When ________ questions in class, one should answer them as clearly as possible.
It was not until I came here ____ I realized this place was famous, for not only its beauty but also its weather.
—How much shall I pay for the phone call? —You________. This is free of charge.