Question

an antigen - presenting cell (apc) is often a
a red blood cell
b macrophage
c helper t cell
d platelet

Explanation:

Antigen - presenting cells (APCs) are a heterogeneous group of immune cells that function to display antigenic peptides on their surface. Macrophages are a type of APC. Red blood cells are mainly involved in oxygen transport. Helper T cells are part of the adaptive immune response but are not typically APCs. Platelets are involved in blood clotting.

Answer:

B. macrophage