Natural use materials that contrast the color and/or texture of the signaling area (rocks, brush, branches, stomped grass).

信号区域中颜色、纹理差异较大的材料（岩石，树林，树枝，践踏过的草地等）

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Key points: texture, structure and classification of sedimentary rocks.

重点：沉积岩的结构、构造和分类。

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Texture and structure of igneous rocks and classification.

岩浆岩的结构和构造岩浆岩的分类。

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