**Core Concept**
Mee's lines are a manifestation of nail changes resulting from certain toxic exposures. They are characterized by transverse white bands or grooves on the nails, indicative of nail plate damage.

**Why the Correct Answer is Right**
Mee's lines are typically associated with arsenic poisoning. Arsenic exposure can cause damage to the nail matrix, leading to the formation of these characteristic transverse bands. This occurs due to the disruption of nail keratinization, a process crucial for nail growth and integrity. Arsenic interferes with the enzymes responsible for keratinization, ultimately resulting in the appearance of Mee's lines.

**Why Each Wrong Option is Incorrect**
**Option A:** Lead poisoning is associated with other systemic manifestations, including neurological and hematological effects, but not specifically with Mee's lines.
**Option B:** Mercury poisoning can cause nail changes, but they are typically more diffuse and not typically described as Mee's lines.
**Option C:** Manganese poisoning can cause neurological and psychiatric symptoms, but it is not characteristically associated with Mee's lines.

**Clinical Pearl / High-Yield Fact**
Mee's lines are a classic sign of arsenic poisoning and should be considered in the differential diagnosis of patients with occupational exposure to marine timbers or other arsenic-containing materials.

**Correct Answer: A. Arsenic poisoning.**