**Core Concept**
Chronic arsenic poisoning occurs due to prolonged exposure to arsenic, leading to accumulation of arsenic and its metabolites in the body. This can cause various systemic effects, including skin lesions, cardiovascular disease, and neurological damage. The diagnosis of arsenic poisoning relies on laboratory tests that can detect the presence of arsenic or its metabolites in biological samples.

**Why the Correct Answer is Right**
The laboratory examination of choice for chronic arsenic poisoning involves the analysis of urine, hair, and nails. Arsenic and its metabolites can be detected in the urine, which is the most common specimen used for diagnosis. Hair and nails can also be analyzed for arsenic content, as they can accumulate arsenic over time. However, blood is not a common specimen used for the diagnosis of chronic arsenic poisoning, as arsenic levels in blood may not accurately reflect the body's burden of arsenic.

**Why Each Wrong Option is Incorrect**
* **Option A:** Urine is a common specimen used for the diagnosis of chronic arsenic poisoning, as it can detect the presence of arsenic and its metabolites.
* **Option B:** Hair is also a specimen that can be analyzed for arsenic content, as it can accumulate arsenic over time.
* **Option C:** Nails can be analyzed for arsenic content, similar to hair, and can provide a historical record of arsenic exposure.

**Clinical Pearl / High-Yield Fact**
When considering the diagnosis of chronic arsenic poisoning, it's essential to remember that the presence of arsenic in urine, hair, or nails can provide evidence of exposure, but the absence of arsenic in these specimens does not rule out arsenic poisoning. Other diagnostic methods, such as clinical evaluation and imaging studies, may be necessary to confirm the diagnosis.

**Correct Answer:** D. Blood.