challenge: Why is Spix's red-handed howler currently listed as a Vulnerable species by the International Union for Conservation of Nature?
  
  A. Due to overhunting by humans
  B. Due to a population increase of over 50% over the past 3 generations
  C. Due to climate change affecting their food supply
  D. Due to habitat loss resulting in a population decrease of over 30% over the past 3 generations
  Answer: 