In an experiment,freshly hatched larvae of an insect (Khapra beetle) were reared on a basal diet (complete diet without cholesterol) with increasing amounts of cholesterol. Results obtained are shown in the given graph.
The graph indicates:

• A
  Cholesterol is an essential dietary requirement of Khapra beetle
• B
  Growth of Khapra beetle is directly proportional to cholesterol concentration
• C
  Cholesterol concentration of $2 \; \mu g/g$ diet is the optimum level
• D
  Growth of Khapra beetle is inhibited when cholesterol concentration exceeds $2 \; \mu g/g$ diet