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 70-year-old woman collapses suddenly after ambulating to the bathroom from her hospital bed. At autopsy she has the gross pathologic finding shown here. Which of the following conditions is the most likely risk factor for development of this woman's immediate cause of death? <image 1> 
A. Blunt chest trauma
B. Inhalation of inorganic dusts
C. Prolonged immobilization
D. Bronchopneumonia

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
A 70-year-old woman collapses suddenly after ambulating to the bathroom from her hospital bed. At autopsy she has the gross pathologic finding shown here. Which of the following conditions is the most likely risk factor for development of this woman's immediate cause of death? <image 1> 
A. Blunt chest trauma
B. Inhalation of inorganic dusts
C. Prolonged immobilization
D. Bronchopneumonia

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