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 53-year-old man suffers a cardiac arrest and his wife calls paramedics, who arrive a few minutes later and begin resuscitative measures. A regular heart rate is established after about 40 minutes of resuscitative efforts as he is being transported to the hospital. A thrombolytic agent is administered on admission. Which of the following cellular changes is most likely to now be occurring within his myocardium? <image 1> 
A. Apoptosis
B. Free radical injury
C. Heterophagocytosis
D. Squamous metaplasia

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 53-year-old man suffers a cardiac arrest and his wife calls paramedics, who arrive a few minutes later and begin resuscitative measures. A regular heart rate is established after about 40 minutes of resuscitative efforts as he is being transported to the hospital. A thrombolytic agent is administered on admission. Which of the following cellular changes is most likely to now be occurring within his myocardium? <image 1> 
A. Apoptosis
B. Free radical injury
C. Heterophagocytosis
D. Squamous metaplasia

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