Which of the Following Statements Best Describes the "Two-Signal Requirement

Which of the following statements best describes the "two-signal requirement" for naive lymphocyte activation?

A) Lymphocytes must recognize two different antigens to become activated.
B) Lymphocytes must recognize the same antigen at two sequential times to become activated.
C) Lymphocytes must recognize antigen and respond to another signal generated by microbial infection to become activated.
D) Both naive B and naive T lymphocytes must simultaneously recognize antigen for either to be activated.
E) When lymphocytes recognize antigen, the antigen receptors must activate two-signal transduction pathways to become activated.