There are many different categories of t-cells that carry out various roles for the immune system. differentiation for most t-cells occurs during the t-cell maturation, but some differentiation occurs after maturation following antigen presentation. one type of t-cell's functioning is dependent on antigen presentation and provides the immune system with continued protection against past pathogens. what is this category of t-cell? a) t b) memory t c) cytotoxic t d) natural killer t