6．
| A．indicator | B．predict | C．process | D．movement | E．a(chǎn)dapt | F．tracked |
| G．formation | H．deliberate | I．similar | J．a(chǎn)dvantageous | K．surprised | |
Dogs Used to Be More Like Cats
Researchers studying fossils （化石） of the early ancestors of dogs that lived up to 40million years ago believe the predators （捕食性動(dòng)物） evolved as a direct consequence of climate change．The study claims the （41）C transformed man's best friend from a creature that behaved more like a cat，into the canine （犬） we know and love today．
Ancestors of dogs living in North America 40million years ago were ambush （伏擊式） predators-in a（n） （42）I way to cats'．But a million years later，the thick forest that once covered the continent began to give way to grasslands．This led to a（n） （43）G in the body shape and hunting behavior of dogs，turning them into animals that no longer （44）K their prey （獵物），but chased it down instead．
This evolutionary transition was （45）F by the scientists who examined the elbows and teeth of 32species of dogs that lived between 40million and two million years ago．
"The elbow is a really good （46）A of what carnivores （食肉動(dòng)物） are doing with their forelimbs （前肢），which tells their entire （47）D abilities，"said Brown University's Christine Janis，who led the study．
The research was based on an analysis of fossil specimens （標(biāo)本） in the American Museum of Natural History in New York．It suggests dog evolution was directly related to climate change．After all，it was not （48）J to operate as a pursuit-and-pounce predator until there was room to run．
If predators evolved with climate change over the last 40million years，the authors argue they may continue to （49）E in response to the present global warming trend．In this way，the results of the study could help （50）B how animals may look in the future．
