Gun control is a subject ________ Americans have argued for a long time.
More consumers are waiting for the further drop of housing prices with money in their hands rather than ______ houses, according to a report.
Nobody believed his reason for being absent from the class __________he had to meet his uncle at the airport.
Shall we go ____ downtown to buy some clothes of high quality?
____ we are alone, we can speak freely.
The chairman thought ____ necessary to invite Professor Smith to speak at the meeting.