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 one of the following is an Index of communicability of an Infection? \nSelect and explain. \nA. Carrier rate, B. Prevalence rate, C. Secondary attack rate, D. Primary attack rate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: An\xa0 important\xa0 measure\xa0 of communicability is Secondary attack rate.\nSecondary attack rate (SAR)\xa0 is defined as "the number of exposed persons developing the disease within the range of the\xa0 incubation\xa0 period,\xa0 following\xa0 exposure to the primary case" .\xa0 It is given by the formula :', 'role': 'assistant'}]