In the reaction between hydrogen sulphate ion and water\({\rm{HSO}}_4^ - {\rm{\;}} + {\rm{\;}}{{\rm{H}}_2}0 \to {\rm{\;}} - {\rm{\gg \;}}{{\rm{H}}_3}{0^ + } + {\rm{SO}}_4^{2 - }\)the water acts as:

• A. an acid
• B. a base
• C. a salt
• D. an inert medium