Let $M$ be $2\times 2$ symmetric matrix with integer entries, then $M$ is invertible if

Which of the following matrix is invertible? $A_1=\left[\begin{array}{rr}4& 2\\ 2& 1\end{array}\right]$, $A_2=\left[\begin{array}{ccc}-1& -2& 3\\ 4& 5& 7\\ 2& 4& -6\end{array}\right]$, $A_3=\left[\begin{array}{ccc}1& 0& 0\\ 5& 2& 1\\ 7& 2& 1\end{array}\right]$, $A_4=\left[\begin{array}{lll}1& 0& 1\\ 0& 2& 3\\ 1& 2& 1\end{array}\right]$.