The principle of vaccination or immunization depends on the property of _________of the immune system. The most appropriate word to fill the blank is:

memory

The principle of vaccination or immunization depends on the property of "memory" of the immune system.

Explanation: The correct answer is (a) memory.

Vaccination or immunization is a process that stimulates the immune system to recognize and remember specific pathogens or antigens. When a person is vaccinated, their immune system is exposed to a harmless form of the pathogen or to specific antigens derived from the pathogen. This exposure triggers an immune response, including the production of antibodies and the activation of memory cells.

Memory cells are a vital component of the immune system. They are specialized immune cells that "remember" specific pathogens or antigens that the body has encountered before. When the body is exposed to the same pathogen or antigen in the future, memory cells quickly recognize it and mount a rapid and effective immune response. This response is faster and stronger than the primary immune response that occurs during the initial infection or vaccination.

The presence of memory cells allows the immune system to provide long-term protection against specific pathogens. This is why vaccination is an essential strategy for preventing infectious diseases. By stimulating the immune system to generate memory cells, vaccines help to prepare the body's defenses and provide immunity against future infections by the same pathogen.

Therefore, the principle of vaccination or immunization relies on the property of "memory" of the immune system, enabling it to recognize and mount a rapid immune response against specific pathogens.