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>What is the correct method for constructing the waterproofing layer of the basement exterior wall with coiled materials:<image 1>
A. The roll waterproof layer is laid on the upstream surface of the external wall
B. The roll waterproof layer is laid on the back surface of the external wall
C. The outer wall roll adopts the empty laying method
D.  When laying double layer coils, the two layers of coils are perpendicular to each other

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
A
What is the correct method for constructing the waterproofing layer of the basement exterior wall with coiled materials:<image 1>
A. The roll waterproof layer is laid on the upstream surface of the external wall
B. The roll waterproof layer is laid on the back surface of the external wall
C. The outer wall roll adopts the empty laying method
D.  When laying double layer coils, the two layers of coils are perpendicular to each other

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