(d)
Since, $(x - 2)$ is a common factor of the expressions $x^{2} + ax + b\ and\ x^{2} + cx + d$
$\Rightarrow 4 + 2a + b = 0$ ...(i)
and $4 + 2c + d = 0$ ...(ii)
$\Rightarrow 2a + b = 2c + d$
$\Rightarrow b - d = 2(c - a)$
$\Rightarrow \ \frac{b - d}{c - a} = 2$