题目内容：
Clayton Critcher and David Dunning found that
A．negative feedback produces improvement in people's performance A．negative feedback produces improvement in people’s performance.
A．negative feedback produces improvement in people’s performance.
B．positive affirmations break patterns of negative thoughts
B．positive affirmations break patterns of negative thoughts.
B．positive affirmations break patterns of negative thoughts.
C．a positive mindset can help people to broaden their horizon
C．a positive mindset can help people to broaden their horizon.
C．a positive mindset can help people to broaden their horizon.
D．the truth behind how affirmations work is still not revealed
D．the truth behind how affirmations work is still not revealed.
D．the truth behind how affirmations work is still not revealed.
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答案解析：