Among the following,the calcination process is

• A
  $2 Cu_2S + 3 O_2 \xrightarrow{\Delta} 2 Cu_2O + 2 SO_2 \uparrow$
• B
  $Al_2O_{3(s)} + 2 NaOH_{(aq)} + 3 H_2O_{(l)} \longrightarrow 2 Na[Al(OH)_4]_{(aq)}$
• C
  $2 CuFeS_2 + O_2 \longrightarrow Cu_2S + 2 FeS + SO_2 \uparrow$
• D
  $Fe_2O_3 \cdot x H_2O \xrightarrow{\Delta} Fe_2O_{3(s)} + x H_2O_{(g)}$