当白昼逐渐变短时，制造食物是时间越来越少，树必须靠它的食物生存，有些树不想供养它们的树叶，所以到了秋天就会让树叶脱落。
When the days get shorter, they have less time for making food and the tree must live off its food. Some trees don't want to feed their leaves so they shed their leaves in autumn.
当白昼逐渐变短时，制造食物是时间越来越少，树必须靠它的食物生存，有些树不想供养它们的树叶，所以到了秋天就会让树叶脱落。
When the days get shorter, they have less time for making food and the tree must live off its food. Some trees don't want to feed their leaves so they shed their leaves in autumn.
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