**Core Concept**
Ribavirin is a synthetic nucleoside analog with antiviral properties, primarily used against RNA viruses. Its mechanism of action involves inhibiting viral RNA synthesis and replication.

**Why the Correct Answer is Right**
Ribavirin is effective against respiratory syncytial virus (RSV) by interfering with viral RNA polymerase activity. This leads to a decrease in viral replication and the production of viral progeny. RSV is a major cause of respiratory illness in infants and young children, and ribavirin therapy has been shown to reduce the severity and duration of RSV infection.

**Why Each Wrong Option is Incorrect**
**Option B:** Ribavirin is not effective against herpes simplex virus (HSV), which is typically treated with antiviral agents such as acyclovir or valacyclovir. HSV is a DNA virus, and ribavirin's mechanism of action is more suited to RNA viruses.

**Option C:** Ribavirin is not used to treat hepatitis B, which is caused by the hepatitis B virus (HBV). HBV is a DNA virus, and ribavirin is not effective against it. Treatment for HBV typically involves antiviral agents such as lamivudine or tenofovir.

**Option D:** Ribavirin is not effective against group A coxsackievirus, which is a type of enterovirus. While ribavirin has been used to treat some viral infections, it is not typically used to treat coxsackievirus infections.

**Clinical Pearl / High-Yield Fact**
When treating viral infections with ribavirin, it is essential to note that this agent should be used under close medical supervision due to its potential toxicity and interactions with other medications.

**✓ Correct Answer: A. Respiratory syncytial virus**