We use the Stefan-Boltzman law for the rate at which a blackbody emits radiation:
$\begin{align*}\frac{\Delta Q}{\Delta t} = \epsilon \sigma A T^4\end{align*}$
$T \to 2 T$ means that $\Delta Q/\Delta t \to 16 \Delta Q/\Delta t$ . Therefore, answer (D) is correct.

Solution to 2008 Problem 8