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>A case-control study of the association between drinking surface water and rectal cancer was conducted by a person who, considering that place of residence may be a potential confounding factor when analysing the association between drinking different types of water and rectal cancer, further divided the place of residence into rural and urban areas, and obtained the data in the table below.<image 1> The adjusted OR was
A. 4.52
B. 2.0
C. 1.26
D. 3.45

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
B
A case-control study of the association between drinking surface water and rectal cancer was conducted by a person who, considering that place of residence may be a potential confounding factor when analysing the association between drinking different types of water and rectal cancer, further divided the place of residence into rural and urban areas, and obtained the data in the table below.<image 1> The adjusted OR was
A. 4.52
B. 2.0
C. 1.26
D. 3.45

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