The colours are magnificent, but the question of exactly why some trees turn yellow or orange, and others red or purple, is something which has long puzzled scientists.
这些颜色很瑰丽，但究竟为什么有些树会变成黄色或橙色，而有些树会变成红色或紫色，这个问题一直困扰着科学家。
Why do newspapers turn yellow over time?
随着时间的流逝，报纸为什么会变黄呢？
They turn yellow along the way and are ready to be sold.
它们在路上变黄，准备好被出售了。
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