**Core Concept**
The question is testing the student's knowledge of viral characteristics, specifically the stability of viruses in different environmental conditions. Viral stability is crucial for their transmission and survival in various settings.

**Why the Correct Answer is Right**
The correct answer is a virus that is labile to acid (more susceptible to degradation in acidic environments) but heat stable (resistant to denaturation by heat). This characteristic is typical of viruses with a lipid envelope, such as influenza viruses. The lipid envelope of these viruses makes them more susceptible to acidic pH, which can disrupt the membrane and inactivate the virus. However, heat stability is due to the presence of a lipid envelope, which also protects the viral genome from heat-induced denaturation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect because it does not accurately describe the viral stability characteristics mentioned in the question.
* **Option B:** This option might be incorrect because it could describe a virus that is both acid and heat labile, which does not match the description provided in the question.
* **Option D:** This option might be incorrect because it could describe a virus that is both acid and heat stable, which is not consistent with the characteristics mentioned in the question.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that viruses with a lipid envelope, such as influenza, are more susceptible to acidic environments, which can inactivate them. This characteristic is crucial for understanding the transmission and survival of these viruses in different settings.

**Correct Answer: C. Influenza virus**