Next, define class Screen, including a friend declaration for clear.

其次，定义类的屏幕，包括一个明确的朋友宣言。

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Folding Screen, including Canvas Screen, Leather Screen and Wooden Screen;

包含帆布家具，皮革家具和木家具等；

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Folding Screen, including Canvas Screen, Leather Screen and Wooden Screen;

包含帆布家具，皮革家具和木家具等；

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