Which symptom best signals possible head gasket failure?

• A. White exhaust, milky oil, coolant loss with external leaks.
• B. Overheating due to thermostat failure.
• C. White exhaust, milky oil, coolant loss with no external leaks, overheating, and low compression or misfire in multiple cylinders.
• D. Oil odor noticeable only during cold starts.

Answer: (C)