During the formation of $N_2O_4$ from $NO_2$,the odd electrons on two $NO_2$ molecules pair up to form ............

• A
  a weak $N-N$ bond,two equal $N-O$ bonds,and two other unequal $N-O$ bonds.
• B
  a weak $N-N$ bond and four equal $N-O$ bonds.
• C
  a weak $N-N$ bond and four unequal $N-O$ bonds.
• D
  a strong $N-N$ bond and four equal $N-O$ bonds.