The present age of father and son at present is $12x$ years and $5x$ years respectively.
Now, $12x – 5x = 28$
$\implies 7x = 28$
$\implies x = 4$
$\therefore $ Father present age $ = 12x = 48$ years and son present age $ = 5x = 20$ years.
Now, the required ratio $ = \dfrac{48+8}{20+8} = \dfrac{56}{28} = \dfrac{2}{1}$
Hence, the ratio of their ages after eight years $ = 2:1.$
So, the correct answer is $(C).$