**Core Concept**
The question is testing the concept of antiviral therapy, specifically the mechanism of action of certain drugs that inhibit viral replication. Post-translational modification of viral proteins is a crucial step in the viral life cycle, and drugs that target this process can effectively inhibit viral replication.

**Why the Correct Answer is Right**
The correct answer is a drug that targets the host cell machinery responsible for post-translational modification of viral proteins. This process involves the addition of phosphate groups to viral proteins, which is essential for their proper functioning. The correct answer works by inhibiting the host cell enzyme responsible for this process, thereby preventing the proper functioning of viral proteins and ultimately inhibiting viral replication.

**Why Each Wrong Option is Incorrect**
**Option A**: This option is incorrect because it targets a different step in the viral life cycle, such as viral entry or replication. While it may be an effective antiviral drug, it does not specifically target post-translational modification of viral proteins.
**Option B**: This option is incorrect because it is a drug that targets a different type of viral protein, such as the viral genome or viral enzymes. It does not specifically target post-translational modification of viral proteins.
**Option C**: This option is incorrect because it is a drug that targets a host cell process, but not specifically post-translational modification of viral proteins.

**Clinical Pearl / High-Yield Fact**
One important thing to remember is that antiviral drugs that target post-translational modification of viral proteins are often effective against a broad range of viruses, making them a valuable tool in the treatment of viral infections.

**Correct Answer: C. Lopinavir**