$4.$ A dome$-$shaped skating hall is under the design phase. The emissivity of the rink surface is $0\mathrm{.}9.$ Two materials are available for the hemispherical roof with the emissivity coefficients $0\mathrm{.}2$ and $0\mathrm{.}8,$ respectively. Which material would you select assuming the temperature of the rink surface is fixed $\backslash (-5^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )?$ Justify your answer briefly.