**Core Concept**
The question tests the understanding of relative risk (RR) and attributable risk (AR) in epidemiological studies, specifically in the context of comparing the effects of two drugs on disease incidence.

**Why the Correct Answer is Right**
Relative risk (RR) is a measure of the ratio of the probability of an event occurring in the exposed group versus the non-exposed group. Attributable risk (AR), on the other hand, represents the proportion of disease incidence in the exposed group that can be attributed to the exposure. The correct answer should relate to the relationship between RR and AR, which is that AR is equal to the product of RR and the prevalence of the disease in the population (P).

**Why Each Wrong Option is Incorrect**
**Option A:** This option might claim that AR is equal to RR, which is incorrect because AR takes into account the prevalence of the disease in the population.
**Option B:** This option might state that AR is equal to the difference in disease incidence between the exposed and non-exposed groups, which is incorrect because AR is a proportion, not a difference.
**Option C:** This option might claim that RR is equal to AR, which is incorrect because RR is a ratio, not a proportion.

**Clinical Pearl / High-Yield Fact**
In epidemiological studies, it's essential to consider the prevalence of the disease in the population when calculating attributable risk, as it provides a more accurate estimate of the proportion of disease incidence that can be attributed to the exposure.

**Correct Answer: A. AR = RR x P**