D-Arabinose, an aldopentose, undergoes Kiliani-Fischer chain extension (HCN, hydrolysis, reduction). The aldohexoses obtained are

AD-glucose and D-galactose
BD-mannose and D-galactose
CD-glucose and D-mannose
DD-glucose and D-fructose

Answer: C

HCN adds to C-1 to give two cyanohydrins that differ only at the new C-2. The old C-2 to C-4 become C-3 to C-5, which match glucose and mannose, so the products are the C-2 epimers D-glucose and D-mannose.

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