Which of the following statements is true regarding the structure of $Cr_2O_7^{2-}$?

• A
  It does not contain $Cr-Cr$ and $O-O$ bonds.
• B
  It contains one $Cr-Cr$ bond and six $O-O$ bonds.
• C
  It contains no $Cr-Cr$ bond and six $O-O$ bonds.
• D
  It contains one $Cr-Cr$ bond and seven $Cr-O$ bonds.