**Core Concept**
The SARS (Severe Acute Respiratory Syndrome) causative agent is a type of virus that belongs to the coronavirus family. The virus primarily targets the respiratory system, causing severe pneumonia and acute respiratory distress syndrome (ARDS).

**Why the Correct Answer is Right**
The SARS causative agent is a member of the coronavirus family, specifically the subfamily Coronavirinae. The virus is thought to be zoonotic, originating from bats before infecting humans. The SARS-CoV virus uses the angiotensin-converting enzyme 2 (ACE2) receptor for entry into host cells, which is primarily expressed in the lungs and other respiratory tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because SARS is not caused by a bacterium, but rather a virus.
**Option B:** This option is incorrect because Influenza is a different type of virus that causes respiratory illness, but it is not the causative agent of SARS.
**Option C:** This option is incorrect because HIV is a retrovirus that targets the immune system, not the respiratory system.

**Clinical Pearl / High-Yield Fact**
The SARS-CoV virus is highly contagious and can be spread through close contact with an infected person, or by touching contaminated surfaces and then touching one's face.

**Correct Answer: C. SARS-CoV**