$A-$ In nature,lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides.
$R-$ Industrial combustion,forest fires,automobile exhausts,and power-generating stations are also sources of atmospheric nitrogen oxides.

• A
  $A$ and $R$ both are correct.
• B
  $A$ and $R$ both are incorrect.
• C
  $A$ is correct and $R$ is incorrect.
• D
  $A$ is incorrect and $R$ is correct.