15. Please draw the molecular structure of the pentapeptide "PNSKV" in the two- dimensional representation of Fisher projection. (5%)

17. Please select (pick out) the aspartic proteases and cysteine proteases, respectively, from the enzymes listed below. (5%) (A) Alanine aminopeptidase, (B) Pepsin, (C) Caspase 1, (D) Renin, (E) Elastase, (F) Thrombin, (G) Trypsin, (H) HIV-1 protease, (I) Carboxy peptidase A, (J) Papain