The first birds appeared during late Jurassic times. These birds are known from    four very good skeletons, two incomple

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问题        The first birds appeared during late Jurassic times. These birds are known from
   four very good skeletons, two incomplete skeletons, and an isolated feather, all from
   the Solnhofen limestone of Bavaria, Germany. This fine-grained rock, which is
   extensively quarried for lithographic stone, was evidently deposited in a shallow
(5)  coral lagoon of a tropical sea, and flying vertebrates occasionally fell into the water
   and were buried by the fine limy mud, to be preserved with remarkable detail In this
   way, the late Jurassic bird skeletons, which have been named Archaeopteryx, were
   fossilized. And not only were the bones preserved in these skeletons, but so also
   were imprints of the feathers. If the indications of feathers had not been preserved in
(10) association with Archaeopteryx, it is likely that these fossils would have been
   classified among the dinosaurs, for they show numerous theropod characteristics.
   Archaeopteryx were animals about the size of a crow, with an archeosaurian type of
   skull, a long neck, a compact body balanced on a pair of strong hind limbs, and a
   long tail. The forelimbs were enlarged and obviously functioned as wings.
(15) Modern birds, who are the descendants of these early birds, are highly
   organized animals, with a constant body temperature and a very high rate of
   metabolism. In addition, they are remarkable for having evolved extraordinarily
   complex behavior patterns such as those of nesting and song, and the habit among
   many species of making long migrations from one continent to another and back
(20) each year. Most birds also have very strong legs, which allows them to run or walk on the
   ground as well as to fly in the air. Indeed, some of the waterbirds, such as ducks and
   geese, have the distinction of being able to move around proficiently in the water, on
   land, and in the air, a range in natural locomotor ability that has never been attained
(25) by any other vertebrate.

选项 A、nesting materials
B、four skeletons in good condition
C、two fragmented skeletons
D、a single feather

答案A

解析
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