Americans love dogs, all types of dogs: small dogs, big dogs, lapdogs  . Each year, people spend billions of dollars on their four-legged pals, making sure the lovable dogs have enough food to eat and lots of toys to play with. Dogs love people, too. They lick their faces, protect their homes. Where did these four-legged companions come from? Some scientists believe that they have found the answer. Scientists have long known that dogs evolved from  wolves. Exactly when the transformation from wolf to dog actually took place, however, remains a mystery. Some said dogs evolved as a separate species 135,000 years ago in two parts of the world. One group of dogs developed in Europe and Asia from Asian wolves. The other group evolved in North, Central, and South America from American wolves. Now researchers say those theories are wrong. New studies suggest that _ dogs first appeared 15,000 years ago in eastern Asia. Scientists also say that every modern dog descended from approximately five female Asian wolves, the mother of all modern dogs. Scientists suspect dogs first set paws in North America by following settlers across a land bridge that once linked northern Asia and North America. From this story, we can conclude that   _  .
dogs are scientists' best friends dogs are more like wolves than they are like any other animal most dogs are from Africa scientists have no idea how dogs evolved