9. Arrange 2016 coins into a triangle. Place 1 coin in the 1st row, 2 coins in the 2nd row, …, and $N$ coins in the $N$th row. Then the sum of the digits of $N$ is $(\quad)$.
(A) 6
(B) 7
(C) 8
(D) 9
(E) 10
9. D.

From the problem, we know
$$
\begin{array}{l}
1+2+\cdots+N=\frac{N(N+1)}{2}=2016 \\
\Rightarrow N=63 \Rightarrow 6+3=9
\end{array}
$$