challenge: According to Swami Vivekananda, what are the characteristics of a true guru?
  
  A. A lack of emotions, and a focus on material possessions
  B. Desire for wealth and fame, and a deep understanding of the physical world
  C. The ability to perform miracles, and a strong desire for power
  D. A pure character, selflessness, and a deep understanding of the scriptures
  Answer: 