No species has developed a closer relationship with humanity than the dog, though cat-love

rs may disagree. But that relationships basis — what it is about dogs that allows them to live【C1】______ with people — is still【C2】______ understood. After all, dogs are【C3】______ from wolves, which are big, scary carnivores that would certainly have【C4】______ with early man for prey, and【C5】______ have been averse to the occasional human as a light snack. 【C6】______ specifically bred for fighting, dogs are more docile than wolves, so that is【C7】______ part of the answer. But mere docility cannot【C8】______ for why people like to have dogs in their homes. Sheep are【C9】______, but few people keep them as pets. Brian Hare, of Harvard University, thinks he knows. And, as he told the American Association for the Advancement of Science meeting in Seattle, it does not【C10】______ well on the intelligence of mankinds closest living【C11】______, the chimpanzee. Dr. Hares hypothesis is that dogs are superbly【C12】______ to social cues from people. That【C13】______ them to fit in with human society. On one【C14】______, this might sound common sense. But humans are such【C15】______ animals that they frequently【C16】______ to realize just how unusual are their own【C17】______ at communicating. Dr. Hare【C18】______ decided to test his idea by【C19】______ the abilities of dogs with those of chimpanzees,【C20】______ are often regarded as second only to people in their level of innate intelligence.

【C1】

A．at present

B．at difference

C．at ease

D．at distance