Certain viruses have evolved to be able to avoid detection by cytotoxic T cells. These viruses remove the MHC class 1 molecules from the surface of the cell that they are infecting. This ensures that the cytotoxic T cells do not bind to the infected cell and kill the cell and the virus within. Which immune cell is specifically designed to recognize these types of viral threats?

• A. CD4 effector cells.
• B. T helper cells.
• C. Regulatory T cells.
• D. Natural killer cells.
• E. CD8 effector cells.