The second within-subject factor is difficulty, included three levels, easy, medium and difficult.

第二个因素是被试内变量，即阅读材料的难度，分为容易、中等、难三个水平。

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There are four difficulty levels like Simple, Medium, Difficult and Challenge.

有四个一样简单，中等，困难和挑战的难度级别。

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There are four difficulty levels like Simple, Medium, Difficult and Challenge.

有四个一样简单，中等，困难和挑战的难度级别。

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