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

• A
  $CO$ is oxidized to $CO_2$ with steam in the presence of a catalyst,and then $CO_2$ is absorbed in an alkali.
• B
  $CO$ and $H_2$ are separated fractionally based on the difference in their densities.
• C
  $CO$ is removed by absorption in an aqueous solution of $Cu_2Cl_2$.
• D
  $H_2$ is separated by absorption in $Pd$.