**Core Concept**
Live vaccines are made from weakened or attenuated pathogens, which provide immunity by stimulating a mild infection. They are often used to protect against viral infections such as measles, mumps, and rubella.

**Why the Correct Answer is Right**
The correct answer is a killed-virus vaccine, which is inactivated or killed, rather than live. Killed-virus vaccines, such as the inactivated influenza vaccine, stimulate an immune response without causing a full-blown infection. This type of vaccine is often used for individuals who cannot receive live vaccines, such as those with weakened immune systems.

**Why Each Wrong Option is Incorrect**
**Option A:** This is a live vaccine, as it contains weakened or attenuated pathogens.
**Option B:** This is a live vaccine, as it contains weakened or attenuated pathogens.
**Option C:** This is a live vaccine, as it contains weakened or attenuated pathogens.

**Clinical Pearl / High-Yield Fact**
Live vaccines are often given in combination to protect against multiple infections, such as the MMR (measles, mumps, and rubella) vaccine.

**Correct Answer: D. Killed-virus vaccine.