Which requires catalyst [AFMC 1987; MP PET 1999]

• A. \[S+{{O}_{2}}\to S{{O}_{2}}\]
• B. \[2S{{O}_{2}}+{{O}_{2}}\to 2S{{O}_{3}}\]
• C. \[C+{{O}_{2}}\to C{{O}_{2}}\]
• D. All