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>Determine the resultant internal normal and shear force in the member at section a-a, which passes through point A. The 500-lb load is applied along the centroidal axis of the member.<image 1>
A. Na=500 lb, Va=250 lb
B. Na=600 lb, Va=0
C. Na=500 lb, Va=0
D. Na=550 lb, Va=0

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
Determine the resultant internal normal and shear force in the member at section a-a, which passes through point A. The 500-lb load is applied along the centroidal axis of the member.<image 1>
A. Na=500 lb, Va=250 lb
B. Na=600 lb, Va=0
C. Na=500 lb, Va=0
D. Na=550 lb, Va=0

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