Final answer:
MHC I molecules present antigens on nucleated cells and infected cells, while MHC II molecules activate T cells by presenting abnormal antigens. The function of MHC I molecules is antigen presentation to cytotoxic T cells.
Step-by-step explanation:
MHC I molecules are expressed on all nucleated cells and are essential for presentation of normal "self" antigens. They also present foreign antigens on MHC I when cells become infected by intracellular pathogens, marking the infected cell for destruction.
In contrast, MHC II molecules are only found on immune system cells, such as macrophages, dendritic cells, and B cells. They present abnormal or nonself pathogen antigens for the initial activation of T cells.
Therefore, the correct answer to the question is b) Antigen presentation to cytotoxic T cells.