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
Incompetent lips refer to 
Select and explain. 
A. Inability of the Lips to cover the incisors in the mandibular relaxed position, B. Inability of the lips to cover the incisors in occlusion, C. The lips come in between the upper and lower incisors, D. Tongue thrusts against the Lips during swallowing
A: Inability of the Lips to cover the incisors in the mandibular relaxed position
Answer: A: Inability of the Lips to cover the incisors in the mandibular relaxed position 
Explanation: None