d
For infinite many solutions
$D=D_{1}=D_{2}=D_{3}=0$
$\operatorname{Now} D =\left|\begin{array}{lll}1 & 1 & 1 \\ 1 & 2 & 3 \\ 1 & 3 & \lambda\end{array}\right|=0$
$1 .(2 \lambda-9)-1 .(\lambda-3)+1 .(3-2)=0$
$\therefore \lambda=5$
$\operatorname{Now} D _{1}=\left|\begin{array}{lll}2 & 1 & 1 \\ 5 & 2 & 3 \\ \mu & 3 & 5\end{array}\right|=0$
$2(10-9)-1(25-3 \mu)+1(15-2 \mu)=0$
$\mu=8$