Rajiv took three substances P, Q, and R and burnt them one by one. He noted down his observations given below. I. Substance P bums quickly producing heat and light. II. Substance Q bums in room temperature on its own. III. Substance R bums with the evolution of heat, light, and sound. Which of the following statements regarding the given information is correct?

• A.  Substances P and Q are undergoing rapid combustion whereas R is undergoing explosion.
• B.  Substances P and R are undergoing spontaneous combustion whereas Q is undergoing rapid combustion.
• C.  Substance P is undergoing rapid combustion, Q is undergoing spontaneous combustion while R is undergoing explosion.
• D.  Substance P is undergoing spontaneous combustion, Q is undergoing rapid combustion while R is undergoing explosion.