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>The following rock mass structure types () do not belong to the "Code for Geological Investigation of Water Resources and Hydropower Engineering" (GB Classification of Rock Mass Structure for 50287-99)<image 1>
A. Overall, block, and sub block structures
B. Giant thick layered, thick layered, medium thick layered, interbedded, and thin layered structures
C. Weathering unloading structure and weathering fragment structure
D. Inlaid fragmented structure and fragmented structure

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
The following rock mass structure types () do not belong to the "Code for Geological Investigation of Water Resources and Hydropower Engineering" (GB Classification of Rock Mass Structure for 50287-99)<image 1>
A. Overall, block, and sub block structures
B. Giant thick layered, thick layered, medium thick layered, interbedded, and thin layered structures
C. Weathering unloading structure and weathering fragment structure
D. Inlaid fragmented structure and fragmented structure

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