Two objects are described below. Which of the following statement is TRUE about these objects?
\[
\begin{array}{c}
f: \mathbb{Z} \rightarrow \mathbb{R}, \quad f(x)=\frac{x \% 3}{((x \% 3)-1)^{2}} \\
g: \mathbb{Z} \rightarrow \mathbb{Z}, \quad g(n)=\left\{\begin{array}{ll}
0 & \text { when } n \text { is odd } \\
1 & \text { when } n \text { is even }
\end{array}\right.
\end{array}
\]
(a) \( g \circ g \) is not defined
(c) Both \( f \) and \( g \) are functions
(b) The domain of \( g \) is \( \{0,1\} \)
(d) \( g \) is a function but \( f \) is not
