Consider the following statements concerning food chains.
$I$. Removal of $80\; \%$ tigers from an area resulted in greatly increased growth of vegetation.
$II.$ Removal of most of the carnivores resulted in an increased population of deers.
$III.$ The length of food chains is generally limited to $3$ to $4$ trophic levels due to energy loss.
$IV.$ The length of food chains may vary from $2$ to $8$ trophic levels.
Which two of the above statements are correct?

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