Let $S$ be the set of all real values of $k$ for which the system of linear equations
$$\begin{aligned}
& x + y + z = 2 \\
& 2 x + y - z = 3 \\
& 3 x + 2 y + k z = 4
\end{aligned}$$
has a unique solution. Then $S$ is\\
(1) an empty set\\
(2) equal to $\mathrm { R } - \{ 0 \}$\\
(3) equal to $\{ 0 \}$\\
(4) equal to $R$