Impetigo can be caused by either Staphylococcus aureus or Streptococcus pyogenes. Culture-based identification of the causative organism can be complicated by _____.
a. the fastidious nature of both organisms
b.the ability of S.aureus to kill S-pyogenes
c.their common optimal growth temperature, 37\deg C
d.the common surface antigens of these two organisms