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
[{'content': 'Which of the following is not an indication for a class II\nactivator: \nSelect and explain. \nA. Mandibular retrusion, B. Horizontal/anterior type of mandibular growth, C. Crowding lower anteriors, D. Upright lower anteriors', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Class-II and III malocclusions, class-I open bite and deep bite malocclusions, children with lack of vertical development in lower facial height, and upright mandibular incisors are indications of activators.\nActivators may produce moderate mandibular rotation (anteriorly down words), so they are contraindicated in vertical growers.', 'role': 'assistant'}]