#### Answer

a. The domain is $C=\{1,2,3,4\}$ and the codomain is $D=\{a,b,c,d\}$.
b. $G(1)=G(2)=G(3)=G(4)=c$

#### Work Step by Step

This function is a constant function. The fact that every value in the domain is mapped onto a single value in the codomain does not conflict with the definition of a function.