Read the following article and answer the question. Article: Dolphins are not fish, but warm-blooded animals. They live in groups, and speak to each other in their own language. In this, they are like other animals, such as bees and birds. But dolphins are very different from almost all land animals. Their brain is nearly the same size as our own, and they live a long time--at least twenty or thirty years. Like some animals, dolphins use sound to help them find their way around. They also make these sounds to talk to each other and to help them find food. We now know they do not use their ears to receive these sounds, but the lower part of the mouth, called the jaw. Strangely, dolphins seem to like man, and for thousands of years there have been stories about the dolphin and its friendship with people. There is a story about sailors in the 19th century. In a dangerous part of the sea off the coast of New Zealand, they learnt to look for a dolphin called Jack. From 1871 to 1903, Jack met every boat in the area and showed it the way. Then in 1903 a passenger on a boat called The Penguin shot and wounded Jack. He recovered and for nine years more continued to guide all ships through the area-except for The Penguin. Today, some people continue to kill dolphins, but many countries of the world now protect them and in these places it is against the law to kill them. Question: Which of the following does the dolphin use to help it find its way around? Answer:
Its mouth.