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>A man at a point P on the shore of a circular lake of radius 1 mile wants to reach the point Q on the shore diametrically opposite P (Fig. 16-5). He can row 1.5 miles per hour and walk 3 miles per hour. At what angle $\theta $ ($0<\theta < \pi /2$) to the diameter PQ should he row in order to minimize the time required to reach Q? <image 1>
A. $\theta = \pi /2$
B. $\theta = \pi /3$
C. $\theta = \pi $
D. $\theta = 2\pi $

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
A man at a point P on the shore of a circular lake of radius 1 mile wants to reach the point Q on the shore diametrically opposite P (Fig. 16-5). He can row 1.5 miles per hour and walk 3 miles per hour. At what angle $\theta $ ($0<\theta < \pi /2$) to the diameter PQ should he row in order to minimize the time required to reach Q? <image 1>
A. $\theta = \pi /2$
B. $\theta = \pi /3$
C. $\theta = \pi $
D. $\theta = 2\pi $

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