Statement (A): If $i^2=-1$ , then $\left|\begin{array}{cc}i& 0\\ 0& -i\end{array}\right|=1$ 

Statement (B): If $\left|\begin{array}{cc}1& 3\\ a& 3\end{array}\right|=9$, then $a=7$

$ad-bc=$ $-i\times i-0\times 0$

$=-i^2-0$

$=-i^2$

$=-\left(-1\right)$

$=1$

$\left|\begin{array}{cc}1& 3\\ a& 3\end{array}\right|=9$

$ad-bc$ $=1\times 3-a\times 3=9$

$3-3a=9$

$-6=3a$

$-2=a$

$\therefore$  $a=-2$