Arectangular open box is to be made from $1m^2$ of cardboard. The maximum volume $($in $m^3)$ of such a box is

a$.\frac{\sqrt[\phantom{2}]{3}}{4}$

b$.\frac{\sqrt[\phantom{2}]{3}}{18}$

c$.\frac{\sqrt[\phantom{2}]{3}}{6}$

d$.3\sqrt[\phantom{2}]{3}$

e$.\frac{\sqrt[\phantom{2}]{3}}{9}$