## **Core Concept**
The question tests knowledge of antiviral drugs, specifically those used in the treatment of both Hepatitis B and HIV. This requires understanding the pharmacotherapy of viral infections, particularly the drugs that have a broad spectrum of activity against these viruses.

## **Why the Correct Answer is Right**
Tenofovir is a nucleotide reverse transcriptase inhibitor (NtRTI) used in the treatment of HIV infection. It is also effective against Hepatitis B virus (HBV) and is used in the treatment of chronic HBV infection. Tenofovir works by inhibiting the reverse transcriptase enzyme of HIV and the DNA polymerase enzyme of HBV, thereby reducing viral replication. Its dual activity makes it a valuable option for patients co-infected with HIV and HBV.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While specific drugs are listed, without the actual drug names provided, we can infer based on common knowledge that not all antiretroviral or antiviral drugs have activity against both viruses.
- **Option B:** Similarly, another drug might have activity against one or the other but not both.
- **Option C:** This could be a distractor representing a drug with activity against one of the viruses but not both.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Tenofovir** is one of the few drugs that has activity against both HIV and HBV, making it a crucial component in the management of patients with co-infections. This dual activity is particularly important in regions with high prevalence rates of both infections.

## **Correct Answer:** D. Tenofovir