A 14-year-old boy complains of a fever of 38-39 C that has been observed for the last 5 days, runny nose, and sore throat. Examination detects signs of catarrhal stomatitis, tonsillitis, and pharyngitis and enlarged lymph nodes along the sternocleidomastoid muscle that resemble a chain and are mobile and mildly painful. The palatine tonsils are sharply hyperemic and covered in a plaque that can be easily removed. Make the provisional diagnosis.