Extraction of a metal $(M)$ from its sulfide ore $(M_2S)$ involves the following chemical reactions:
$2M_2S + 3O_2 \xrightarrow{\text{heat}} 2M_2O + 2SO_2 \uparrow$
$M_2S + 2M_2O \xrightarrow{\text{heat}} 6M + SO_2 \uparrow$
The metal $(M)$ may be

• A
  $Zn$
• B
  $Cu$
• C
  $Fe$
• D
  $Ca$