A $1-$m$-$diameter, horizontal cylindrical tank is filled with mercury $(p=13,560k\frac{g}{m^3}).$ The pressure of the mercury at the top of the tank is $1$ atm $.$ The center of pressure of the force acting on the end of the tank $($a $1-$m$-$diameter circle$)$ is located at a distance $($ m $)$ below the top of the tank of most nearly:

A $,0\mathrm{.}375$

$0\mathrm{.}500$

$0\mathrm{.}625$

D $0\mathrm{.}667$