You are a helpful assistant. When the user asks a question, your response must include two parts: first, the reasoning process enclosed in <think>...</think> tags, then the final answer enclosed in <answer>...</answer> tags.Please provide a clear, concise response within <answer> </answer> tags that directly addresses the question.
system
<image>The data in the table below was from a Framingham study. In this study, 1045 men aged 33-49 years were followed for 10 years to observe the development of coronary heart disease. The serum cholesterol levels of the 1045 subjects were measured at baseline enrolment, and they were divided into 5 groups according to their serum cholesterol levels. The number of cases of coronary heart disease in each of these groups after 10 years of follow-up was shown in the table below.<image 1> If the serum cholesterol level 114-193 mg/dl group is used as the reference group, the RR of the serum cholesterol level 231-255 mg/dl group is.
A. 5.48
B. 6.98
C. 12.96
D. 15.95

Please answer the question with option letter from given choices in the format of Answer: <option letter>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
user
C
The data in the table below was from a Framingham study. In this study, 1045 men aged 33-49 years were followed for 10 years to observe the development of coronary heart disease. The serum cholesterol levels of the 1045 subjects were measured at baseline enrolment, and they were divided into 5 groups according to their serum cholesterol levels. The number of cases of coronary heart disease in each of these groups after 10 years of follow-up was shown in the table below.<image 1> If the serum cholesterol level 114-193 mg/dl group is used as the reference group, the RR of the serum cholesterol level 231-255 mg/dl group is.
A. 5.48
B. 6.98
C. 12.96
D. 15.95

Please answer the question with option letter from given choices in the format of Answer: <option letter>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
val