Sulphur trioxide can be obtained by which of the following reaction :

Question

( A ) $S+H_2SO_4\underrightarrow{\qquad \Delta \qquad }$
( B ) $Fe_2+(SO_4)_3\underrightarrow{\qquad \Delta \qquad }$
( C ) $H_2SO_4+PCI\underrightarrow{\qquad \Delta \qquad }$
( D ) $CaSO_2+C\underrightarrow{\qquad \Delta \qquad }$