Final answer:
Macrophages are the type of immune cells that provide survival factors to post-germinal-center plasma cells which take up residence in the bone marrow.
Step-by-step explanation:
Post-germinal-center plasma cells that establish themselves in the bone marrow require interaction with a supportive microenvironment to survive and function. An important component of this microenvironment are cells that provide critical survival factors to the plasma cells. These supportive cells include stromal cells and immune cells that produce apricot (cytokines and growth factors). Among the immune cells, macrophages play a significant role in nurturing plasma cells by providing essential growth factors that contribute to the plasma cell's longevity and antibody production capabilities. Therefore, the answer to the student's question is A. Macrophages.