**Core Concept**
Killed vaccines contain inactivated pathogens and are not capable of causing disease. They are used to stimulate an immune response without live virus replication. The distinction between killed and live vaccines lies in the presence of viable, replicating organisms.

**Why the Correct Answer is Right**
The **17-D Vaccine** is a **live attenuated vaccine** used for polio, not a killed vaccine. It contains a weakened form of the poliovirus that replicates in the body, leading to a stronger and longer-lasting immune response. In contrast, **Salk (inactivated polio vaccine)**, **Hepatitis B vaccine**, and **HDCV (Hepatitis C vaccine)** are all **killed or inactivated** vaccines. Hepatitis B uses recombinant technology with inactivated HBsAg, and HDCV is a killed hepatitis C vaccine (though less common). Thus, 17-D is the only live vaccine here.

**Why Each Wrong Option is Incorrect**
Option A: Salk vaccine is a **killed polio vaccine** made with inactivated poliovirus.
Option B: Hepatitis B vaccine uses **inactivated hepatitis B surface antigen (HBsAg)**, so it is a killed vaccine.
Option D: HDCV (Hepatitis C vaccine) is a **killed vaccine** containing inactivated viral particles.

**Clinical Pearl / High-Yield Fact**
Remember: **"Live = 17-D, Sabin"** — all live attenuated vaccines (like 17-D) are **not** killed. Always check if the vaccine contains viable, replicating organisms.

✓ Correct Answer: C. 17-D Vaccine