24. Define $\operatorname{gcd}(a, b)$ as the greatest common divisor of integers $a$ and $b$. Given that $n$ is the smallest positive integer greater than 1000 and satisfies:
$$
\begin{array}{l}
\operatorname{gcd}(63, n+120)=21, \\
\operatorname{gcd}(n+63,120)=60 .
\end{array}
$$

Then the sum of the digits of $n$ is ( ).
(A) 12
(B) 15
(C) 18
(D) 21
(E) 24