Passage Summary: Most people have an enzyme that clears nicotine from their systems. People with the most common version of this enzyme tend to smoke more than others. This is because the faster nicotine leaves your body, the sooner you want another cigarette.

Conclusion: The most common form of the CYP2A6 enzyme is the one that eliminates nicotine from the body most rapidly.

Reasoning: Smokers with the common form of the enzyme smoke more frequently, and faster nicotine elimination leads to more frequent cravings.

Analysis: To complete this explanation, we need to connect the 'common form' of the enzyme mentioned in the second sentence to the 'faster elimination' mentioned in the third. If the common form is indeed the most efficient at clearing nicotine, it explains the higher smoking frequency. Look for an answer that establishes this specific link between the common enzyme and high-speed nicotine processing.