Americans have many expressions ___(used, using) the word “dogs”. Nowadays people in the United States love their dogs and ______(threat, treat)them well. They take their dogs ____(for , on ) walks,let them ____(played, play) outside, and give them good food and ______(medicine, medical) care . However, dogs without owners to care _____(about, for) them lead a different kind of life. The expression “to lead a dog’s life”describes a person _____(who, whom)has ______(a, an) unhappy existence.