Read the following passage and answer the questions that follow:

Animals communicate with one another in many interesting ways. These may consist of signs, gestures, looks, sounds, smells or even light produced by the body. Song and dance are the other means of communication.

When faced with danger, animals warn others using signals such as mock charges, grimaces or sound. They also call their mates, inform other members of the group about the source of food, advertise territory and 'teach' the young the ways of the world. Baby birds call their parents for help and attention and demand food.

Far from being a silent world, the ocean is a noisy place. Fishes, molluscs, sea lions, walruses, whales and dolphins chatter away in the waters using a variety of sounds-whistles, squeaks, clicks and groans which range from low pitch to ultrasonic sounds beyond the range of human hearing. Whales and dolphins are sometimes called the 'musicians of the sea' as birds are of the sky.