Which of the following statements about the depletion of ozone layer is correct?

• A
  The problem of ozone depletion is less serious at poles because $NO_2$ solidifies and is not available for consuming $ClO^{\bullet}$ radicals.
• B
  The problem of ozone depletion is more serious at poles because ice crystals in the clouds over poles act as catalyst for photochemical reactions involving the decomposition of ozone by $Cl^{\bullet}$ and $ClO^{\bullet}$ radicals.
• C
  Freons,chlorofluorocarbons,are inert. Chemically,they do not react with ozone in stratosphere.
• D
  Oxides of nitrogen also do not react with ozone in stratosphere.