Because he howls or whines in the presence of impending death, the dog was once thought to have supernatural powers and believed to be capable of seeing gods and ghosts invisible to men. Actually, the basis for these beliefs lies in the hound' s sensibility to people' s feelings and his superior hearing ability and sense of smell, which enable him to detect signs hidden from human observation. His record of saving lives is outstanding, for he often gives warning of fire and other dangers not noticed by his master.
The dog's major contribution, however, has been to medical research. Both his diet and his structure are comparable to those of the human being, and so he has been the subject of countless demonstrations and experiments. Open-heart surgery has been made possible largely because of the dog. But his sacrifice has repaid his own species as well by safeguarding it from rabies (狂犬病), distemper, and other diseases.
The dog has always been noted for, ______.

A. protecting children
B. assisting shepherds
C. helping hunters
D. herding cattle