题目

  Along the river banks of the Amazon and the Orinoco there lives a bird that swims before it can fly, flies like a fat chicken, eats green leaves, has the stomach of a cow and has claws(爪)on its wings when young .They build their homes about 4.6m above the river ,an important feature(特征)for the safety of the young. It is called the hoatzin.     In appearance，the birds of both sexes look very much alike with brown on the back and cream and red on the underside .The head is small, with a large set of feathers on the top, bright red eyes, and blue skin. Its nearest relatives are 在等比数列｛an｝中，a1=－1,