根据以下材料，回答40-43题
The dog has always been considered man´s best friend．Always noted for being particularly faithful in watching over children,he also has his place by the fireside, in the cow pasture,on the sheep range(放牧区),and beside the hunter in forest．He is easy to train,works hard,and often performs astonishing feats．And in the frozen polar regions he was once the principal motive power,before being lately displaced by the plane and helicopter.
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 iris 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 no-ticed 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．
Dogs are similar to human beings in ．

A size

B structure

C temperament

D appearance