____is certain is ___prevention is more important than treatment .
I love _____ history because it gives us _____ knowledge of past event.
Parents complain that _____ shown on TV will have bad influence on high school students’ moral _____.
A box of _____ is a most welcome gift for one’s lover on Valentine’s Day.
The 1930s were the year when he wrote one _____ after another, and when his first collection of _____ was published.
In this research, two are _____, and the others are _____.