Answer:
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Pioneer species are the first organisms to live in an area
Some examples of a pioneer are:
•bunch grass
•milkweed
•queen Anne’s lace
•Sphagnum moss
•sedge
•pitcher plant
A. <span>Exposure to an antigen
Exposure to viruses and antigens led to the foundation of modern vaccination. Vaccination introduces an antigenic material that helps the ability of the immune system to adapt a specific pathogen, therefore leading to a long-term immunity.</span>