A 5 year old child who has not had routine pediatric care develops a febrile disease with cough and a blotchy rash, and is brought to the emergency room. On physical examination, there is cervical and axillary lymphadenopathy.Also noted is an erythematous, maculopapular rash behind the ears and along the hairline, involving the neck and, to a lesser extent, the trunk. Examination of this patient's oropharynx would likely reveal which of the following lesions?