Impetigo is due to an infection caused by

A) Staphylococcus aureus but not Streptococcus pyogenes.
B) Streptococcus pyogenes but not Staphylococcus aureus.
C) either Staphylococcus aureus or Streptococcus pyogenes.
D) neither Staphylococcus aureus nor Streptococcus pyogenes.