This will not only keep the study habit ____ but also keep you up to date on your class assignments . 

 After two years’ research, we now have a ____ better understanding of the disease.

—The guard keeps         watch at the gate.—So he does. Only those         knows well could be let in.

As the light turned green, I stood for a moment, not _____, and asked myself what I was going to do.

English has been very popular because it is the _______ language in many western countries.