$A$ sulphide ore is first converted into its oxide before reduction. This is done because

• A
  $A$ sulphide ore cannot be reduced to metal at all
• B
  No reducing agent is found suitable for reducing a sulphide ore
• C
  The enthalpy of formation of $CO_2$ is more negative than that of $CS_2$
• D
  $A$ metal oxide is generally more stable than the metal sulphide