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': 'Apical collar signifies: \nSelect and explain. \nA. Retentive form, B. Resistance form, C. Both 1 & 2, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: ΑPICΑL COLLAR\xa0= Retentive form (usually nearly 2 mm of parallel walls at apical region)\xa0\nKeyword is\xa0TUG BACK.', 'role': 'assistant'}]