d
Here $\mathrm{D}=\left|\begin{array}{ccc}2 & 1 & 1 \\ 1 & -1 & 1 \\ 1 & 1 & \mathrm{a}\end{array}\right|$
$=2(-\mathrm{a}-1)-1(\mathrm{a}-1)+1+1$
$=1-3 \mathrm{a}$
$\mathrm{D}_{3}=\left|\begin{array}{ccc}2 & 1 & 5 \\ 1 & -1 & 3 \\ 1 & 1 & \mathrm{~b}\end{array}\right|$
$=2(-b-3)-1(b-3)+5(1+1)$
$=7-3 b$
for $a=\frac{1}{3}, b \neq \frac{7}{3}$, system has no solutions