**Core Concept**
SARS (Severe Acute Respiratory Syndrome) is a viral respiratory illness caused by a coronavirus, specifically SARS-CoV. The pathogenesis involves the virus binding to angiotensin-converting enzyme 2 (ACE2) receptors in the lungs, leading to inflammation and respiratory failure.

**Why the Correct Answer is Right**
The correct answer is related to the epidemiology and transmission dynamics of SARS. SARS-CoV was first identified in Guangdong province, China, and then spread to other countries through human-to-human transmission, primarily through respiratory droplets and close contact with infected individuals. The virus was found to be highly contagious and had a mortality rate of approximately 9.6%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because SARS-CoV was not primarily found in this region during the outbreak.
**Option B:** This option is incorrect because while SARS-CoV did spread to other countries, it was not most common in this region.
**Option C:** This option is incorrect because SARS-CoV was not most common in this region during the initial outbreak.

**Clinical Pearl / High-Yield Fact**
SARS-CoV is a zoonotic virus, meaning it can be transmitted from animals to humans, and it is believed to have originated from an animal source, possibly bats or palm civets.

**Correct Answer: D. Guangdong province, China.**