Captive animals are often kept in poor (a)________ inhuman conditions. In the worst zoos animals are still displayed (b)________ the entertainment of the public.(c)_________ animals are placed in impoverished and unsuitable surroundings, (d)________ often behave in normal and neurotic ways. It is common for polar bears (e)_______ constantly pace up and down or twist their heads and circle over and over again. The behaviour is now recognized by scientists (f) ________ a sign of stress and frustration.