If the matrix $A=\begin{bmatrix} 3 & 7 & a\\b & 1 & 5\\-2 & c & 11\end{bmatrix}$ is a symmetric matrix, then the values of a, b and c are :

$a=11, b=7, c=1 $ $a=11,b=1, c=7$ $a=-2, b=7,c=5$ $a=-2, b=1,c=7$

$a=-2, b=7,c=5$