Explanation

(d)
Equation of pair straight lines is $xy - x - y + 1 = 0$
$\Rightarrow (x - 1)(y - 1) = 0$
$\Rightarrow x - 1 = 0\ or\ y - 1 = 0$
The intersection points of $x - 1,\ y - 1 = 0$ is (1, 1)
$\because$ Lines $x - 1 = 0,\ y - 1 = 0$ and $ax + 2y - 3 = 0$ are concurrent
$\therefore\$The intersecting points of first two lines lies on the third line $ax + 2y - 3 = 0$
$\therefore a + 2 - 3 = 0\ \Rightarrow a = 1$