Dinitrogen and dioxygen,the main constituents of air,do not react with each other in the atmosphere to form oxides of nitrogen because:

• A
  $N_{2}$ is unreactive under atmospheric conditions.
• B
  Oxides of nitrogen are unstable.
• C
  The reaction between them can only occur in the presence of a catalyst.
• D
  The reaction is endothermic and requires a very high temperature.