28. Which of the following statements are accurate?

A. none of the answers are correct

B. An effective humoral immune response typically requires both T cell and B cell activation.

C. T cells activation does not usually require antigen presentation by an antigen presenting cell.

D. Viruses can avoid activating the adaptive immune system if they do not change their surface antigens once they have been recognized by T and B cells.

E. People who were affected with the smallpox virus before cowpox virus were naturally immune to the smallpox virus because the viruses shared some common antigens and the memory cells that recognized cowpox antigens responded to smallpox antigens as well.

F. Helper T cells can kill cells that are infected with viruses and Cytotoxic T cells are known to activate B cells.