Sort the Following Events to Reflect the Order in Which

Short Answer

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