Fact 1: Active immunity results when an immune response to a pathogen produces memory cells. Fact 2: Pathogens are germs that cause disease. Given the two facts above, answer the question "Active immunity is when an immune response occurs after a germ produces what?" with the following options: - harmful substances - bioaerosols - rapid expansion - Allergies - anemia - it needs them - Chemical energy - memory cells
A:
memory cells