**Core Concept**
Live attenuated vaccines contain a weakened or attenuated form of a pathogen, which triggers a mild infection that stimulates the immune system to produce antibodies and immune cells without causing severe disease. This type of vaccine is often used to prevent diseases such as measles, mumps, and rubella.

**Why the Correct Answer is Right**
The correct answer is a live attenuated vaccine because it contains a weakened form of the influenza virus, which causes a mild infection that stimulates the immune system to produce antibodies and immune cells. This type of vaccine provides long-term immunity against the flu virus and has been shown to be effective in preventing severe illness and hospitalization due to influenza.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because inactivated vaccines contain a killed or inactivated form of the pathogen, which does not cause an infection and instead stimulates the immune system through other mechanisms.
**Option B:** This option is incorrect because toxoids are vaccines that contain a toxin or a part of a toxin, which is inactivated or modified to be harmless.
**Option C:** This option is incorrect because subunit vaccines contain only a small part of the pathogen, such as a protein or sugar, which does not cause an infection and instead stimulates the immune system through other mechanisms.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that live attenuated vaccines should not be given to individuals with weakened immune systems, such as those with HIV/AIDS or undergoing chemotherapy, as they can cause severe illness.

**Correct Answer:** C. Mumps, measles and rubella vaccine is an example of a live attenuated vaccine.