This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
On the day following a formocresol pulpotomy of a
mandibular molar, a three year old patient returned with
a large ulcer near the midline of the lower lip. What is
the probable cause of the ulcer? 
Select and explain. 
A. Lip biting by the patient, B. Allergy to the anaesthetic solution, C. Pressure by the rubber dam frame, D. Leakage of formocresol on the lip
A: Lip biting by the patient
Answer: A: Lip biting by the patient 
Explanation: None