2. Given that $A D$, $B E$, and $C F$ are the altitudes of acute $\triangle A B C$, and $H$ is the orthocenter of $\triangle A B C$. Then $H$ is the ( ) of $\triangle D E F$.
(A) orthocenter
(B) centroid
(C) circumcenter
(D) incenter
2. D.

It is easy to prove that points $A, E, H, F$ are concyclic $\Rightarrow \angle E F H = \angle E A H$. Similarly, $\angle H B D = \angle D F H$. Also, $\angle H B D = \angle E A H$, thus, $\angle E F H = \angle D F H$ $\Rightarrow F H$ bisects $\angle D F E$. Similarly, $E H$ bisects $\angle D E F$. Therefore, $H$ is the incenter of $\triangle D E F$.