What is the Riemann invariant for C+ characteristic line?

• A. J+ = u + ∫\(\frac {dp}{ρa}\) = constant
• B. J+ = u – ∫\(\frac {dp}{ρa}\) = constant
• C. J+ = u + \(\frac {dp}{ρa}\)
• D. J+ = u – \(\frac {dp}{ρa}\)