Autumn means different things to different people. "It all depends on your personality," said British naturalist Richard Mabey. "Personality shapes your view of the season," he said. "You may see it as a fading-away,a packing-up  ,or as a time of packing in another sense--the exciting gathering of resources before a long journey." If this is true,perhaps it tells us a little about,for instance,Thomas Hood,the 19th Century English poet. About November,he wrote: No warmth,no cheerfulness,no healthful ease No shade,no shine,no butterflies,no bees November! On the other hand,another English poet John Keats,already sensing he was seriously ill,was inspired by a late September day to pen one of the most famous poems in the English language,To Autumn. He wrote to a friend afterwards that there was something comforting and healing about it. According to Richard Mabey,Keats has the biological evidence on his side. Autumn is not a time of slowing down,but a time of new beginnings and great movements of creatures. For example,just at the moment that Keats's "gathering swallows" ( in To Autumn)are departing for Africa,millions of creatures are fleeing from the frozen north like Iceland,Greenland and Russia to winter along the east and south coasts of Britain. According to scientists,before falling,the leaves transfer their chlorophyll  and carbohydrates into the woody parts of the tree for safe keeping over winter. What remains is the natural antioxidants   in the leaves: the yellow and orange carotenoids  ,and another protective chemical specially produced for autumn,the bright-red anthocyanin  .High colour is not a signal of deterioration   and decline,but of detox   ability and good health. A century after Keats,the American poet Loren Eiseley wrote in his journal: "Suppose we saw ourselves burning-like maples in a golden autumn. And that we could break up like autumn leaves...dropping their substance like chlorophyll. Wouldn't our attitude towards death be different?" In autumn,leaves turn yellow before falling because   _  .
they can't bear the freezing they can't get enough water from the wood part chlorophyll and carbohydrates have been lost through leaves chlorophyll and carbohydrates have come back to the wood part