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>In an experiment, researchers randomly assigned college students in an introductory calculus class into four groups. All groups were given the same set of questions in an exam, but the exam began with a brief introductory statement that differed for each group, establishing differing expectations for student performance, as follows: Group A: The introduction stated that most students are expected to pass the exam. Group B: The introduction stated that most students are expected to fail the exam. Group C: The introduction included statistics that showed female students performing worse than male students on similar exams. Group D: The introduction contained no information on expected performance. The results of the experiment are given in the bar graph below: <image 1> What phenomenon best explains the performance differences between Groups A and B?
A. Social facilitation
B. Group polarization
C. Self-serving bias
D. Unstable attribution
E. The Pygmalion effect

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
E
In an experiment, researchers randomly assigned college students in an introductory calculus class into four groups. All groups were given the same set of questions in an exam, but the exam began with a brief introductory statement that differed for each group, establishing differing expectations for student performance, as follows: Group A: The introduction stated that most students are expected to pass the exam. Group B: The introduction stated that most students are expected to fail the exam. Group C: The introduction included statistics that showed female students performing worse than male students on similar exams. Group D: The introduction contained no information on expected performance. The results of the experiment are given in the bar graph below: <image 1> What phenomenon best explains the performance differences between Groups A and B?
A. Social facilitation
B. Group polarization
C. Self-serving bias
D. Unstable attribution
E. The Pygmalion effect

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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