A coarse$-$grained soil has a voids ratio $0\mathrm{.}75,$ and specific gravity as $2\mathrm{.}75.$ The critical gradient at which quick sand condition occurs, is

$($A$)0\mathrm{.}25$

$($B$)0\mathrm{.}50$

$($C$)0\mathrm{.}75$

$($D$)1\mathrm{.}00$