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>Blood glucose level is regulated by two antagonistic hormones, glucagon and insulin. The following graph shows the fluctuations in an individual's blood glucose level over a five hour period: <image 1>. From the information provided above and your knowledge of physiology, which of the following statements are appropriate? I. Normal homeostatic mechanisms maintain a glucose concentration of approximately 1 mg/ml. II. Glucagon is released at points A and C. III. The individual eats a meal at point D. IV. Insulin is being released at points B and E.
A. I only
B. I and II only
C. I and IV only
D. I, II, and III only
E. II, III, and IV only

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
Blood glucose level is regulated by two antagonistic hormones, glucagon and insulin. The following graph shows the fluctuations in an individual's blood glucose level over a five hour period: <image 1>. From the information provided above and your knowledge of physiology, which of the following statements are appropriate? I. Normal homeostatic mechanisms maintain a glucose concentration of approximately 1 mg/ml. II. Glucagon is released at points A and C. III. The individual eats a meal at point D. IV. Insulin is being released at points B and E.
A. I only
B. I and II only
C. I and IV only
D. I, II, and III only
E. II, III, and IV only

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