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 storage height of a small homogeneous earth dam is 16m, and the flow network is shown in Figure 1-5. The interval of the water head gradient equipotential lines in the flow network is evenly divided into m=22 (the number of equipotential lines calculated from downstream is shown in the figure). The G point in the earth dam is located on the 20th equipotential line, 11.5m above the ground level. May I ask which of the following options is the closest to the pore water pressure at point G? ()<image 1>
A. 30kPa
B. 45kPa
C. 115kPa
D. 145kPa

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
The storage height of a small homogeneous earth dam is 16m, and the flow network is shown in Figure 1-5. The interval of the water head gradient equipotential lines in the flow network is evenly divided into m=22 (the number of equipotential lines calculated from downstream is shown in the figure). The G point in the earth dam is located on the 20th equipotential line, 11.5m above the ground level. May I ask which of the following options is the closest to the pore water pressure at point G? ()<image 1>
A. 30kPa
B. 45kPa
C. 115kPa
D. 145kPa

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