In aqueous solution,$Na_2SO_3$ is oxidized by air,but $Na_3AsO_3$ is not. However,when air is passed through a solution containing both $Na_2SO_3$ and $Na_3AsO_3$,both are oxidized. This is an example of:

• A
  Positive catalysis
• B
  Negative catalysis
• C
  Induced catalysis
• D
  Autocatalysis