**Core Concept**
The question is testing the student's knowledge of antiviral medications used for the prophylaxis of influenza virus infections. The H1N1 influenza virus is a subtype of the influenza A virus, and antiviral medications can be used to prevent its spread.

**Why the Correct Answer is Right**
The correct answer is Oseltamivir. Oseltamivir is a neuraminidase inhibitor that works by blocking the release of viral particles from infected cells, thus preventing the spread of the virus. It is effective against both seasonal and pandemic influenza A and B viruses, including the H1N1 virus. Oseltamivir is administered orally and is commonly used for the prophylaxis and treatment of influenza virus infections.

**Why Each Wrong Option is Incorrect**
**Option A:** Zanamivir is another neuraminidase inhibitor, but it is administered via inhalation, making it less suitable for prophylaxis in high-risk populations. It is not the preferred choice for H1N1 influenza virus infections.
**Option B:** Amantadine is an adamantane derivative that was used for the prophylaxis and treatment of influenza A virus infections, but it has limited efficacy against H1N1 and other newer strains. Its use has been largely discontinued due to widespread resistance.
**Option C:** Ribavirin is a nucleoside analog that has broad-spectrum antiviral activity, but it is not specifically indicated for the prophylaxis of H1N1 influenza virus infections. It is more commonly used for the treatment of respiratory syncytial virus (RSV) infections.

**Clinical Pearl / High-Yield Fact**
When choosing an antiviral medication for prophylaxis, consider the route of administration, efficacy against the specific virus strain, and potential side effects. Oseltamivir is a convenient and effective option for H1N1 influenza virus infections, but its use should be guided by local epidemiology and treatment guidelines.

**Correct Answer:** C. Oseltamivir.