**Core Concept**
OPV (Oral Poliovirus Vaccine) is a live, attenuated vaccine used for the prevention of poliomyelitis. The vaccine contains a weakened form of the poliovirus and is administered orally to induce immunity against the disease. The usability of OPV lots is crucial to ensure the vaccine's potency and safety.

**Why the Correct Answer is Right**
The usability of OPV lots is determined by the presence of certain indicators, such as the presence of residual infectious poliovirus or the presence of the Sabin strain of poliovirus. The correct answer is the OPV lot that meets the World Health Organization (WHO) criteria for usability, which includes the absence of residual infectious poliovirus and the presence of the Sabin strain. This is crucial to ensure the vaccine's safety and efficacy.

**Why Each Wrong Option is Incorrect**
* **Option A:** This OPV lot may contain residual infectious poliovirus, making it unusable according to WHO criteria.
* **Option B:** The absence of the Sabin strain in this OPV lot renders it unusable, as the vaccine relies on the presence of this strain to induce immunity.
* **Option D:** This OPV lot may have been exposed to heat or other environmental factors that could compromise its potency and safety.

**Clinical Pearl / High-Yield Fact**
It is essential to follow WHO guidelines for the usability of OPV lots to ensure the safety and efficacy of the vaccine. This includes regular monitoring of the vaccine's potency and the presence of residual infectious poliovirus.

**Correct Answer: C.**