challenge: Why is it generally not correct to specify G as a melodic note in the key of D major, even if its pitch is the same as F#?
  
  A. Because it is never correct to use enharmonic equivalents in music notation
  B. Because G and F# have different pitches in twelve tone equal temperament
  C. Because G is a black key on the piano and F# is a white key
  D. Because F# is diatonic to D major, while G is not
  Answer: 