Use the Gram-Schmidt process to determine an orthonormal basis for $\mathbb{R}^3$ starting with the following sets of vectors:
(a) $\left(\begin{array}{l}1 \\ 0 \\ 1\end{array}\right),\left(\begin{array}{l}1 \\ 1 \\ 1\end{array}\right),\left(\begin{array}{r}-1 \\ 2 \\ 1\end{array}\right)$;
(b) $\left(\begin{array}{l}1 \\ 1 \\ 0\end{array}\right),\left(\begin{array}{r}0 \\ 1 \\ -1\end{array}\right),\left(\begin{array}{r}1 \\ 0 \\ -1\end{array}\right)$;
(c) $\left(\begin{array}{l}1 \\ 2 \\ 3\end{array}\right),\left(\begin{array}{l}4 \\ 5 \\ 0\end{array}\right),\left(\begin{array}{r}2 \\ 3 \\ -1\end{array}\right)$.