Which of the following is true for the industrial production of hydrogen from water gas $(CO + H_2)$?

• A
  $CO$ is removed by absorption in $CaCl_2$ solution.
• B
  $H_2$ is removed by absorption on the surface of $Pd$ metal.
• C
  $CO$ is oxidized to $CO_2$ using steam,and $CO_2$ is absorbed in an alkali.
• D
  $CO$ and $H_2$ are separated by fractional distillation based on their density difference.