Which one of the statements concerning the equilibrium shown is true?

• A
  The two structures are enantiomers of each other. They have equal but opposite optical rotations and racemize slowly at room temperature.
• B
  The two structures are enantiomers of each other. They racemize too rapidly at room temperature for their optical rotations to be measured.
• C
  The two structures are diastereomers of each other. Their interconversion is called mutarotation.
• D
  The two structures are diastereomers of each other. Their interconversion does not require breaking and making bonds,only a change in conformation.