The below slab $-$ section at top and plan to the bottom $-$ is designed to sit on a grid of $12$ in wide by $14$ in deep beams with $f_y=60$ksi&$f_c^{\text{'}}=4$ksi, and normal weight concrete has been used all the way.

Based on this information, the minimum slab thickness should be:

$($A$)5\mathrm{.}0$ in

$($B$)7\mathrm{.}0$ in

$($C$)8\mathrm{.}5$ in

$($D$)9\mathrm{.}5$ in