**Core Concept**
Live vaccines contain a weakened or attenuated form of the pathogen, which stimulates the immune system to produce a specific response without causing the full-blown disease. This type of vaccine is effective in inducing long-term immunity and is often used for diseases such as measles, mumps, and rubella.

**Why the Correct Answer is Right**
The correct answer is a killed-virus vaccine, which means it contains inactivated or killed pathogens that cannot replicate or cause disease. Killed-virus vaccines, like the influenza vaccine, induce an immune response but may not provide lifelong immunity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a live attenuated vaccine, which means it contains a weakened form of the pathogen that can still replicate and cause a mild infection.

**Option B:** This option is incorrect because it is also a live attenuated vaccine, similar to option A.

**Option C:** This option is incorrect because it is a live attenuated vaccine, which is a type of live vaccine.

**Clinical Pearl / High-Yield Fact**
It's essential to note that live vaccines can cause vaccine-associated complications, especially in immunocompromised individuals. Therefore, it's crucial to administer live vaccines with caution and consider the recipient's immune status.

**Correct Answer:** D.