The trees form a natural protection from the sun's rays.
树木起天然的保护作用，遮挡了阳光的照射。
The radiation comes from space (cosmic rays) as well as natural radioactive materials found in the soil, water and air.
辐射来自于外层空间（宇宙射线），以及在土壤，水和空气中的天然放射性物质。
Exposure to UVB rays found in natural and artificial sunlight.
来自自然和人造阳光中的UV B射线照射。
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