$2\mathrm{.}11($extra bonus $5\%)$ Two identical silver spheres of mass m and radius r are placed a distance R $($sphere $1)$ and $2$R $($sphere $2)$ from the Sun, respectively. The ratio of the pressure of solar radiation on sphere $2$ to that on sphere $1$ is a$.0\mathrm{.}25.$ b$.0\mathrm{.}50.$ c$.1\mathrm{.}0.$ d$.2\mathrm{.}0.$ e$.4\mathrm{.}0.$