How does the body builds resistance to certain pathogens

How the body builds resistance to certain pathogens when it comes in contact with the pathogen itself.

Explanation:

Our body develops resistance to pathogens. This is when we allow our bodies to come into contact with certain types of pathogens and our immune systems respond by producing antibodies and the body's defense cells. An example of this can be seen in influenza vaccines. These vaccines bring our body into contact with an inactivated influenza virus molecule, so our immune system will try to fight off this molecule and allow us to become resistant to the pathogen.

answer; i believe the answer is moderate level;

where are the choices