By the end of the last month, I _____________ all the CDs of Justin Bieber.

It is useful to be able to predict the extent _____ a price change willaffect supply and demand.

Please call me ______ 8989766. [ ]

I hear it won’t be ______ he graduates from the university.

In communication, a smile is usually ______ strong sign of a friendly and ______ open attitude.