Which one of the following reactions is an example of calcination process ?

Question

( A ) $MgCO_3 \to MgO + CO_2$
( B ) $2ZnS + 3O_2 \to 2ZnO + 2SO_2$
( C ) $2Ag + 2HCl + (O) \to 2AgCl + H_2O$
( D ) $2Zn+O_2 \to 2ZnO$