Find All Numbers for Which the Rational Expression Is Not $\frac{\mathrm{C}-6}{3}$

Find all numbers for which the rational expression is not defined.
- $\frac{\mathrm{C}-6}{3}$

A) None
B) $\mathrm{c}=6$
C) $\mathrm{c}=0$
D) $\mathrm{c}=-6$