7. In an acute triangle $ABC$ with sides $a, b, c$, the distances from the circumcenter to the three sides are $m, n, p$, respectively. Then $m: n: p$ equals
(A) $\frac{1}{a}: \frac{1}{b}: \frac{1}{c}$;
(B) $a: b: c$;
(C) $\cos A: \cos B: \cos C$;
(D) $\sin A: \sin B: \sin C$.
7. (C)

Let $O$ be the circumcenter of $\triangle A B C$, $O A=O B=O C=R$, (as shown in the figure),
$$
\begin{aligned}
\frac{m}{R}= & \cos \frac{1}{2} \angle B O C=\cos A, \\
\therefore \quad m & =R \cos A .
\end{aligned}
$$

Similarly, $n=R \cos B, p=R \cos C$.
$$
\therefore \quad m: n: p=\cos A: \cos B: \cos C \text {. }
$$