Which of the following statements concerning immunity is correct?

A) Adaptive immunity responses to pathogens improves over time due to generation of memory, which includes an increase in the number of lymphocytes that respond faster than during the original infection.
B) Adaptive immunity demonstrates memory, meaning each lymphocyte responds to a particular pathogen, but responds similarly with each infection.
C) Adaptive immunity demonstrates specificity, which means that lymphocytes only destroy viruses and ignore all other types of pathogens.
D) All of the choices are correct.

Adaptive immunity improves over time due to the generation of memory cells, which results in a faster and more effective response to pathogens that the body has previously encountered. This is because the number of lymphocytes that can respond to the pathogen increases, and these cells respond more quickly than they did during the initial infection. Choices B and C are incorrect because adaptive immunity does demonstrate memory, but the response can become more efficient with subsequent infections, and adaptive immunity is not limited to viruses but can target a wide range of pathogens with specificity.