challenge: What is the systematic name of the enzyme 11-cis-retinol dehydrogenase?
  
  A. 11-cis-retinol:FAD+ oxidoreductase
  B. 11-cis-retinol:NAD+ oxidoreductase
  C. 11-cis-retinol:CoA oxidoreductase
  D. 11-cis-retinol:NADP+ oxidoreductase
  Answer: 