How does a vaccine use antigens to aid the immune system

A vaccine works by training the immune system to recognize and combat pathogens, either viruses or bacteria. To do this, certain molecules from the pathogen must be introduced into the body to trigger an immune response. These molecules are called antigens, and they are present on all viruses and bacteria.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

the answer is b. glad to .