Article: Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are a source of meat.

Now answer this question: What is the most common phrase, or nickname, used by people in the United States to describe dogs in general?
man's best friend
In the article, it is mentioned that "dogs perform many roles for people" and have a big impact on human society. It then states, "...in some cultures dogs are a source of meat". The next sentence says: "This impact on human society has given them the nickname 'man's best friend' in the Western world.".