A vaccine put into the body weakened/dead pathogenic material, which by itself is incapable of causing disease. How does it help to protect the body in the case of infection by a live pathogen

familiarity

Explanation: your bodies immune system remebers past aliments in case it faces them again so a vaccine in your body helps your body build up immunity to the ailment before it overwelhms you like a guy took small amounts of black mamba venom until his immune sysste was so used to  it he could take a bite and survive unscaved

answer; ////increased water pollution; ///////////////////////

it's c. (to reduce the greenhouse effect/carbon gasses)