**Core Concept**
Acute Hepatitis B is caused by the Hepatitis B virus (HBV), which can lead to liver inflammation and damage. The presence of HBsAg (Hepatitis B surface antigen) in the patient's serum is indicative of an active HBV infection. To confirm the diagnosis and assess the severity of the infection, additional investigations are required.

**Why the Correct Answer is Right**
The next best confirmatory investigation for acute Hepatitis B is to test for HBeAg (Hepatitis B e-antigen) and anti-HBc IgM (Immunoglobulin M antibody to Hepatitis B core antigen). HBeAg is a marker of viral replication and infectivity, while anti-HBc IgM indicates recent infection. **Option** **C** is the correct answer because it assesses both viral replication and the presence of a recent infection.

**Why Each Wrong Option is Incorrect**
* **Option A:** HCV (Hepatitis C virus) testing is not relevant in this scenario, as the patient's serum tested positive for HBsAg, indicating an HBV infection.
* **Option B:** Anti-HBs (antibody to Hepatitis B surface antigen) testing is not sensitive for acute HBV infection, as it may not be detectable in the early stages of the disease.

**Clinical Pearl / High-Yield Fact**
In patients with acute HBV infection, it is essential to assess for liver function and the presence of co-infections, such as hepatitis C or D, which can impact the management and prognosis of the disease.

**Correct Answer:** C. HBeAg and anti-HBc IgM.