**Core Concept:**
Hepatitis B infection is a viral disease that affects the liver. It is primarily caused by the Hepatitis B virus (HBV). Active replication refers to the synthesis of viral DNA as part of the infection process. In the context of HBV, this is marked by the presence of viral DNA polymerase, which is an enzyme involved in DNA replication.

**Why the Correct Answer is Right:**
In Hepatitis B infection, active replication is indicated by the presence of viral DNA polymerase. DNA polymerase is an essential enzyme involved in the replication of the HBV genome. During the active replication phase, the HBV genome is replicated, leading to the production of new viral particles and the spread of infection.

**Why Each Wrong Option is Incorrect:**
A. **Option A:** Viral protein synthesis is not a direct indicator of active replication. While proteins are synthesized during the infection, it is not specific enough to determine the stage of infection or active replication.
B. **Option B:** Hepatitis C infection is another viral hepatitis but has distinct clinical, serological, and virological features. In Hepatitis B, active replication is indicated by viral DNA polymerase, not interferon.
C. **Option C:** Interferons are cytokines produced in response to viral infections, particularly in the immune response. They do not directly indicate active replication in Hepatitis B infection.
D. **Option D:** Hepatitis A infection is another viral hepatitis but has distinct clinical, serological, and virological features. In Hepatitis B, active replication is indicated by viral DNA polymerase, not necroinflammation.

**Clinical Pearl:**
Understanding the role of viral DNA polymerase in Hepatitis B infection is crucial for diagnosing active replication and guiding clinical decisions. The presence of viral DNA polymerase indicates the active viral replication phase, which justifies the initiation of antiviral therapy to suppress viral replication and reduce the risk of liver damage and long-term complications.