A mature naive T cell receives "Signal 1" but not "Signal 2" while interacting with an antigen- presenting cell (APC). What could explain this observation? a) The APC cannot present peptide on MHC-II. b) The T cell does not express the correct cytokine receptors. c) The APC has not detected the presence of a pathogen, and does not express co-stimulatory molecules. d) The T cell does not express a TCR capable of binding to any peptide::MHC complexes on the APC..