challenge: What is the condition for a holomorphic vector bundle over a Riemann surface to be stable, according to the Narasimhan-Seshadri theorem?
  
  A. It comes from a reducible projective unitary representation of the fundamental group
  B. It has a trivial fundamental group
  C. It comes from an irreducible projective unitary representation of the fundamental group
  D. It has a non-trivial first Chern class
  Answer: 