老师们报告说，参加成长型思维课的学生中，有27%的学生的积极性发生了显著的变化，而对照组中只有9%的学生的积极性有所变化。

Teachers reported significant motivational changes in 27% of the children in the growth mind-set workshop as compared with only 9% of students in the control group.

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这种极性的变化导致列车前方牵引列车前进的电磁场，同时列车后面的电磁场加上了更多的向前推力。

This change in polarity causes the magnetic field in front of the train to pull the vehicle forward, while the magnetic field behind the train adds more forward thrust.

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直流直流是指没有正负极性往复变化的电流。

Direct current (DC) Direct current is current with no reversals in polarity.

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