Q.Which type of lymphocyte, upon re-exposure to the same antigen, mounts a rapid secondary immune response because of immunological memory?
(A) Neutrophils
(B) Memory B and T cells
(C) Eosinophils
(D) Platelets

Memory cells are the biological basis of both natural re-immunity and vaccination.

Memory B and T cells are formed during the primary immune response to a given antigen and persist long after the original infection has cleared. Because they already "recognise" that specific antigen, a second exposure allows them to proliferate and act immediately, producing a rapid, strong secondary immune response — this is the property called immunological memory.

Neutrophils and eosinophils (options A and C) are cells of the innate immune system; they respond in essentially the same non-specific way to every exposure and do not carry antigen-specific memory. Platelets (option D) are involved in blood clotting, not in immune memory.

Recognise that the phrase 'remembers' and 'rapid secondary immune response' in the question are the exact defining features of immunological memory, which is specifically a property of acquired immunity's memory B and T cells.

Do not select neutrophils or eosinophils — although both are important immune cells, they belong to the innate immune system and act without memory, responding the same way on every single exposure.