Which of the following catalyst is used in the polymerisation of \[CH\equiv CH\] to \[{{C}_{6}}{{H}_{6}}\] [CPMT 1999]

• A. \[AlC{{l}_{3}}\]
• B. \[HgS{{O}_{4}}\]
• C. \[NbC{{l}_{3}}\]
• D. HCl