**Core Concept**
The underlying principle being tested is the concept of attributable risk, which is a measure of the risk of a disease or outcome attributable to a specific exposure. Attributable risk is used in epidemiology to quantify the impact of a particular risk factor on the development of a disease.

**Why the Correct Answer is Right**
To calculate the attributable risk, we first need to determine the incidence of lung cancer among the exposed and unexposed populations. The incidence among the exposed is 20/2000 = 0.01, and among the unexposed is 8/8000 = 0.001. The attributable risk is then calculated as the difference in incidence between the exposed and unexposed groups, which is 0.01 - 0.001 = 0.009.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the formula for calculating attributable risk.
**Option B:** This option is also incorrect as it miscalculates the attributable risk.
**Option D:** This option is incorrect because it does not apply to the given scenario.

**Clinical Pearl / High-Yield Fact**
Attributable risk is a crucial concept in epidemiology, helping to establish the relationship between a risk factor and a disease. It is essential to understand how to calculate and interpret attributable risk to make informed decisions in public health.

**Correct Answer:** C. 0.009