Read the following statements carefully and select the correct ones.
$I.$ $UV$ rays are essential for the production as well as degradation of ozone gas.
$II.$ Ozone present in the ionosphere acts as a shield absorbing $UV$ radiation coming from the sun.
$III.$ One-fourth of the incoming solar radiation is reflected by the atmospheric gases and clouds,and only half of the incoming solar radiation falls on the earth's surface,heating it. Of this,only a small portion is reflected back.

• A
  $I$ and $II$
• B
  $I$ and $III$
• C
  $II$ and $III$
• D
  $I, II$ and $III$