Final answer:
C. Helper T (TH) cell
Helper T (TH) cells are activated by macrophages that present antigens on their surfaces, using MHC II molecules to initiate an immune response during a viral infection.
Step-by-step explanation:
The type of cell activated in lymphatic tissue by macrophages presenting antigens during a viral infection is the Helper T (TH) cell. Macrophages that have phagocytized pathogens display fragments of these pathogens on their surfaces using Major Histocompatibility Complex (MHC) molecules. Specifically, MHC II molecules interact with Helper T-cells, leading to their activation. Helper T cells then facilitate the activation of other immune cells, including both cytotoxic T cells, which directly destroy virally infected cells, and B cells, which can differentiate into plasma cells to produce antibodies.