Find all values of $a, b$, and $c$ for which the following matrices are symmetric:
(a) $\left(\begin{array}{cc}3 & a \\ 2 a-1 & a-2\end{array}\right)$,
(b) $\left(\begin{array}{ccc}1 & a & 2 \\ -1 & b & c \\ b & 3 & 0\end{array}\right)$,
(c)
$$
\left(\begin{array}{ccc}
3 & a+2 b-2 c & -4 \\
6 & 7 & b-c \\
-a+b+c & 4 & b+3 c
\end{array}\right) .
$$