Which of the following statements are correct regarding a food chain?
$(a)$ If $80\%$ of tigers are removed from an area,the growth of vegetation in that area increases.
$(b)$ If carnivores are removed from an area,the population growth of deer increases.
$(c)$ The length of a food chain is limited to $3$ to $4$ trophic levels because the amount of energy decreases in the ecosystem.
$(d)$ The length of a food chain is usually $2$ to $8$ trophic levels.

• A
  Statements $(b)$ and $(c)$ are correct.
• B
  Statements $(c)$ and $(d)$ are correct.
• C
  Statements $(a)$ and $(d)$ are correct.
• D
  Statements $(a)$ and $(b)$ are correct.