For thousands of years, people have lived with dogs. Ancient paintings on the walls of caves show people living with dogs. Almost a third of the homes in the United States and England have dogs, and these dogs come in a wide variety of shapes and sizes. The largest dog in the world was a dog named Zorba. When Zorba, a _ , was seven years old in 1989, he was 94 centimeters (37 inches) tall. In other words, Zorba was more than half as tall as an adult man. At his largest, Zorba weighed more than a heavy weight boxer at 156 kilograms(343 pounds). In comparison, the smallest bog was a Yorkshire terrier from England. This dog was only the size of a matchbox, measuring 7.1 centimeters(2.8 inches) tall and 9.5 centimeters (3.75 inches) from nose to tail. It weighed about half as much as a common book, and even a young child could easily pick it up with one hand. It passed away in 1945 when it was only two years old. Some dogs are wonderful, not for their sizes, but for their brains. One incredible  dog is Endal, the companion   of a man named Allen Parton who has used a wheelchair since a car accident in 1991. In 2001, Parton was hit by a car while crossing a road with Endal, and thrown out of his chair. Endal quickly moved Parton into the recovery place, covered him with a blanket , and pushed his mobile phone close enough for him to reach. Then, once he saw that Parton was all right, Endal ran back and forth to a nearby hotel, barking until people came out to help. Endal was rewarded for his bravery by being awarded a medal, and he has been the subject of a number of TV documentaries. The world's smallest dog weighed half as much as  _   according to the passage.
a child's hand a matchbox a common book a car