When col. lemon arrived at the hospital, the staff determined that his blood had been mistyped, and he was in fact blood type ab-. which of our three suspects could safely donate blood to col. lemon now?

Whoever is -ab can donate blood to lemon. However an +O can give blood to anyone.

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.