**Core Concept**
The positive zone of enamel caries refers to the area within the carious lesion where the enamel has been demineralized, leading to the formation of dentin. This zone is characterized by a distinct histological appearance.

**Why the Correct Answer is Right**
The dark zone, also known as the positive zone, is the area within the carious lesion where the enamel has been demineralized, leading to the formation of dentin. This zone is characterized by a darker appearance under a microscope due to the presence of dentin tubules and the absence of enamel rods. The dark zone is formed as a result of the acid production by the bacteria, which demineralizes the enamel and leads to the formation of dentin. The dentin tubules in this zone are open, allowing for the passage of bacteria and other substances.

**Why Each Wrong Option is Incorrect**
**Option A:** The translucent zone is the area within the carious lesion where the enamel is still intact but has been demineralized. It is characterized by a lighter appearance under a microscope.

**Option C:** The body of the lesion refers to the entire carious lesion, including the dark and translucent zones.

**Option D:** The surface zone is the outermost layer of the carious lesion, where the enamel is still intact but has been demineralized.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize the different zones of enamel caries to understand the progression and severity of the lesion. The dark zone is a critical area where dentin formation occurs, and its recognition can help in the early detection and treatment of carious lesions.

**✓ Correct Answer: B. Dark zone**