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 W 8 X 28 beam of a length 10 ft is held between immoveable supports. The beam has a modulus of elasticity E = 29,000 ksi and coefficient of thermal expansion $\alpha=6.5\times10^{-6}/^\circF$ . If the temperature of the beam is raised uniformly by an amount $\Delta T=20^\circF$ , calculate the thermal stress $\sigma_{T}$ in the beam.<image 1>
A. -2.77 ksi
B. -3.77 ksi
C. -4.77 ksi

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 W 8 X 28 beam of a length 10 ft is held between immoveable supports. The beam has a modulus of elasticity E = 29,000 ksi and coefficient of thermal expansion $\alpha=6.5\times10^{-6}/^\circF$ . If the temperature of the beam is raised uniformly by an amount $\Delta T=20^\circF$ , calculate the thermal stress $\sigma_{T}$ in the beam.<image 1>
A. -2.77 ksi
B. -3.77 ksi
C. -4.77 ksi

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