Because he gave out bad scents (cents).
He wrote "1 + 0 = 0" and then spent the rest of the lesson trying to rub one out...
I'm-in-a-cent!
Because they don't make any cents.
The dime had more cents.
Because they are very scentimental.
Let us spray
A: Question marks.
Criminal: I answered an ad that said "Make money at home."