challenge: In the context of theta characteristics on a curve C of higher genus g, what is one such divisor class?
  
  A. The class of -P, where P is any point on the curve
  B. The class of -Q, where Q is any point on the curve
  C. The class of -S, where S is any point on the curve
  D. The class of -R, where R is any point on the curve
  Answer: 