**Core Concept**
The key concept here is the differentiation between El Tor and classical biotypes of Vibrio cholerae, a bacterium that causes cholera. The El Tor biotype is known for its ability to cause a milder form of the disease compared to the classical biotype.

**Why the Correct Answer is Right**
The correct answer lies in the fact that El Tor vibrio can be differentiated from classical vibrio by its inability to produce a hemolysin called "choleragenoid" which is produced by classical vibrio. This is due to the absence of a specific enzyme called "choleragenoid" in El Tor vibrio. El Tor vibrio also has a lower level of toxin production compared to classical vibrio. The El Tor biotype has a more stable and longer-lasting infection compared to the classical biotype.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not mention any specific characteristic that differentiates El Tor from classical vibrio.

**Option B:** This option is incorrect as it is not a specific characteristic of El Tor vibrio.

**Option C:** This option is incorrect as it is a characteristic of classical vibrio, not El Tor vibrio.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the El Tor biotype of Vibrio cholerae is more commonly found in Asia and Africa, whereas the classical biotype is more commonly found in India and other parts of South Asia.

**Correct Answer: C. Its inability to produce choleragenoid.**