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 flat aluminum alloy bar is fixed at both ends. Segment AB has a slight taper. If the temperature of the bar is raised uniformly by an amount $\Delta T=20^\circF$, find reactions at A and C.Assume that L = 3 ft, t = 1/4 in., b1=2in.,b2=2.5in., E=10,400 ksi, and the coefficient of thermal expansion $\alpha=13\times10^{-6}/^\circF$.<image 1>
A. $R_{A}=R_{C}=-2.429kips$
B. $R_{A}=R_{C}=-1.429kips$
C. $R_{A}=R_{C}=-0.429kips$

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
A flat aluminum alloy bar is fixed at both ends. Segment AB has a slight taper. If the temperature of the bar is raised uniformly by an amount $\Delta T=20^\circF$, find reactions at A and C.Assume that L = 3 ft, t = 1/4 in., b1=2in.,b2=2.5in., E=10,400 ksi, and the coefficient of thermal expansion $\alpha=13\times10^{-6}/^\circF$.<image 1>
A. $R_{A}=R_{C}=-2.429kips$
B. $R_{A}=R_{C}=-1.429kips$
C. $R_{A}=R_{C}=-0.429kips$

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