Sort the following events to reflect the order in which they occur in the presentation of viral peptides to cytotoxic T cells by a virus-infected cell. Your answer would be a four-letter string composed of letters A to D only, e.g. BDCA.
(A) Peptide transport into the ER lumen
(B) Partial proteasomal degradation of the viral protein into peptide fragments
(C) Peptide binding to class I MHC protein in the ER lumen
(D) The appearance of viral protein in the cytosol