Which of the following is true regarding the structural difference between D-mannose and D-glucose?

• A. D-mannose has a different configuration at carbon 2 compared to D-glucose.
• B. D-mannose has a ketone group at carbon 2.
• C. D-mannose is an L-sugar while D-glucose is a D-sugar.
• D. D-mannose has a different configuration at carbon 4 compared to D-glucose.

Answer: (A)