## Core Concept
The question pertains to a historical observation of a specific health issue related to the residents of Naples, characterized by brownish-colored stains. This scenario is associated with a condition caused by an excess of a particular element in the drinking water.

## Why the Correct Answer is Right
The correct answer, **B.**, refers to the condition known as "Brown Piedmont" or more commonly related to, **Mottled enamel** or **Dental fluorosis**. Dr. J.M. Eager's observation in Naples (though more famously associated with Frederick McKay's work in Colorado, USA, and later research in Naples and other areas) relates to the early identification of **fluorosis**. This condition arises from excessive intake of fluoride, particularly during enamel formation in teeth, leading to brownish or yellowish discoloration.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not correspond to the known historical or medical terms associated with the description provided.
- **Option C:** Similarly, this option does not align with recognized medical or historical references to conditions characterized by brownish-colored stains due to environmental factors like water quality.
- **Option D:** This option is also incorrect as it does not relate to the condition described or recognized in medical literature.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **dental fluorosis**, or the condition described, is a **marker of excess fluoride exposure** during tooth development. This condition can range from mild to severe and is an important consideration in public health discussions about water fluoridation and dental health.

## Correct Answer Line
**Correct Answer: B.**