Let $A$ and $B$ be two $3 \times 3$ non-zero real matrices such that $A B$ is a zero matrix. Then\\
(1) The system of linear equations $A X = 0$ has a unique solution\\
(2) The system of linear equations $A X = 0$ has infinitely many solutions\\
(3) $B$ is an invertible matrix\\
(4) $\operatorname { adj } ( A )$ is an invertible matrix