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 true regarding the second number of the instrument formula? \nSelect and explain. \nA. Indicates the primary cutting edge angle, B. The angle is expressed as a percent of 360 degrees, C. This number is always 50 or less, D. It can be omitted to give 3 number code', 'role': 'user'}, {'content': "Answer: C \nExplanation: The second number of a four-number code indicates the primary cutting edge angle, measured from a line parallel to the long axis of the instrument handle in clockwise centigrades.\nThe angle is expressed as a percent of 360 degrees (e.g., 85 = 85% x 360 degrees = 306 degrees).\nThe instrument is positioned, so that this number always exceeds 50.\nIf the edge is locally perpendicular to the blade, then this number is normally omitted, resulting in a three-number code.\n\nRef: Sturdevant's art and science of operative dentistry,\xa04th edition page 311", 'role': 'assistant'}]