51) Which of the following is a reducing sugar? A) a-D-fructofuranose B) the methyl glycoside of cellobiose C) ethyl ẞ-D-glucopyranoside D) methyl a-D-fructofuranoside E) none of the above. 52) Two D-aldopentoses give the same D-aldotetrose upon Ruff degradation. The two aldopentoses are: A) enantiomers. B) meso compounds. C) C2 epimers. D) C4 epimers. E) D-glucose and D-galactose. 53) Which of the following bond arrangements is not commonly found in naturally occurring disaccharides? A) a 1,4' link B) a 1,6' link C) a 1,1' link D) a 1,5' link E) both B and C 54) What peptide remains after two sequential Edman degradations of the pentapeptide Ser-Pro-Gly-Phe-Arg? A) Pro-Gly-Phe B) Ser-Pro-Gly C) Gly-Phe-Arg D) Pro-Gly E) Phe-Arg