The temperatures of two large parallel plates of equal emissivity are $900 \mathrm{~K}$ and $300 \mathrm{~K}$. A reflection radiation shield of low emissivity and negligible conductive resistance is placed parallelly between them. The steady-state temperature of the shield, in $\mathrm{K}$, is
- $759$
- $559$
- $659$
- $859$