Step 1: HP means Harmonic Progression.
If \( a, b, c \) are in HP, then their reciprocals are in AP. Using the properties of harmonic progression, the equation simplifies to a harmonic progression.
Step 2: Conclusion.
Thus, \( \frac{a}{b+c}, \frac{b}{c+a}, \frac{c}{a+b} \) will form a harmonic progression.
Final Answer:
\[
\boxed{C}
\]