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>Write the Fourier series for the three voltage waveforms in (a) of <image 1>.
A. (4 / \pi) (sin \pit + (1 / 2) sin 3\pit + (1 / 4) sin 5\pit + ....).
B. (4 / \pi) (sin \pit + (1 / 3) sin 3\pit + (1 / 5) sin 5\pit + ....).
C. (4 / \pi) (sin \pit + (1 / 2) sin 2\pit + (1 / 4) sin 4\pit + ....).
D. (4 / \pi) (sin \pit + (1 / 3) sin 2\pit + (1 / 5) sin 4\pit + ....).

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
B
Write the Fourier series for the three voltage waveforms in (a) of <image 1>.
A. (4 / \pi) (sin \pit + (1 / 2) sin 3\pit + (1 / 4) sin 5\pit + ....).
B. (4 / \pi) (sin \pit + (1 / 3) sin 3\pit + (1 / 5) sin 5\pit + ....).
C. (4 / \pi) (sin \pit + (1 / 2) sin 2\pit + (1 / 4) sin 4\pit + ....).
D. (4 / \pi) (sin \pit + (1 / 3) sin 2\pit + (1 / 5) sin 4\pit + ....).

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.
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