Final answer:
Myeloid dendritic cells are the most effective at presenting antigens to naive T cells because they are professional antigen-presenting cells specialized for this purpose, expressing high levels of class II MHC molecules and co-stimulatory molecules.
Step-by-step explanation:
The cell type that is best at presenting antigens to naive T cells is myeloid dendritic cells. Dendritic cells play a crucial role in the immune response by taking up antigens in peripheral sites and migrating to lymphoid organs where they present the antigens to naive T cells. These antigen-presenting cells (APCs) are known as professional APCs because they express class II MHC molecules specialized for this task. While macrophages and B cells are also capable of presenting antigens, dendritic cells are the most effective in activating naive T cells. This is due to their high expression of MHC class II molecules as well as co-stimulatory molecules required for naive T cell activation.
The cell type that is best at presenting antigens to naive T cells is d. B-cells. B-cells are part of the immune system and are considered 'professional' antigen-presenting cells, along with macrophages and dendritic cells. They have the ability to present antigens specifically for the purpose of activating T cells.