Recall the Wien displacement law, which states that
$\begin{align*}\lambda_{\text{max}} \cdot T = 2.9 \cdot 10^{-3} \mbox{ m K}\end{align*}$
where $\lambda_{\text{max}}$ is the wavelength emitted by a blackbody at temperature $T$ at which the intensity is a maximum. From this, we can easily find the temperature given the $\lambda_{\text{max}} \approx 2 \;\mu\mathrm{m}$ from the graph:
$\begin{align*}T = \frac{2.9 \cdot 10^{-3} \mbox{ m K}}{\lambda_{\text{max}}} = \frac{2.9 \cdot 10^{-3} \mbox{ m K}}{2 \;\mu\m...$
Therefore, answer (D) is correct.

Solution to 2001 Problem 63