**Core Concept**
Live attenuated vaccines contain a weakened or attenuated form of a pathogen, which induces a mild infection in the recipient and stimulates an immune response without causing the full-blown disease. This type of vaccine is often used for diseases such as measles, mumps, and rubella.

**Why the Correct Answer is Right**
The correct answer is likely to be a vaccine that contains a weakened or attenuated form of a pathogen. Live attenuated vaccines work by inducing a mild infection in the recipient, which stimulates the immune system to produce antibodies and immune cells that can recognize and attack the pathogen. This type of vaccine is often used for diseases where a strong immune response is needed to prevent the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely to be a killed-virus vaccine, which contains a pathogen that has been inactivated or killed. Killed-virus vaccines do not contain a live pathogen and therefore do not induce a mild infection in the recipient.
**Option B:** This option is likely to be a subunit vaccine, which contains only a specific component of the pathogen, such as a protein or sugar. Subunit vaccines do not contain a live pathogen and therefore do not induce a mild infection in the recipient.
**Option C:** This option is likely to be a conjugate vaccine, which combines a weakened pathogen with a carrier protein to enhance the immune response. While conjugate vaccines can be used for live attenuated pathogens, the term "live attenuated" specifically refers to a vaccine that contains a weakened or attenuated form of a pathogen.

**Clinical Pearl / High-Yield Fact**
Live attenuated vaccines can cause mild side effects, such as fever or rash, but they are generally safe and effective. However, they should not be given to individuals with weakened immune systems, as they can cause serious complications.

**Correct Answer: C. MMR (Measles, Mumps, and Rubella) vaccine.**