Which of the following pairs represent a pair of diastereomers?

• A
  Meso tartaric acid and $(l)$-tartaric acid
• B
  The pair of structures:
  $HOOC-CH(OH)-CH(OH)-COO^-$ and $HOOC-CH(OH)-CH(OH)-COO^-$
• C
  The pair of structures:
  $CH_3-CH_2-CH(CH_3)-O-CO-CH(OH)-CH_3$ and $CH_3-CH_2-CH(CH_3)-O-CO-CH(OH)-CH_3$
• D
  All of these