challenge: What is the primary purpose of the extra egg(s) produced by siblicidal bird parents, according to the Insurance Egg Hypothesis (IEH)?
  
  A. To reduce the energy expenditure of the parents
  B. To provide nutrition for the first chick
  C. To serve as a backup in case the first egg fails to hatch or the chick dies soon after hatching
  D. To increase the chances of attracting a mate
  Answer: 