Read the following interview with Dr John Bass, an international shark  specialist who has spent many years studying sharks: First of all, doctor, are all sharks dangerous?   No, they aren't. There are about 250 different kinds of sharks, but fewer than 30 of them are dangerous to humans. Certain sharks are very aggressive   and we should fear them, but the danger of shark attacks is much lower than most people think.   So which sharks are dangerous?   The Great White shark is the most dangerous. Then there is the Tiger shark, which other sharks are afraid of, and the Blue shark. Both of them are very fast and dangerous.   Which are the biggest and smallest sharks?   The Whale shark is the biggest shark in the world. It grows up to 15 m in length and weighs as much as six large cars. The smallest shark, which is found near prefix = st1 /Japan, could fit into the palm of your hand because it is only 15-20 cm long.   Do all sharks have teeth ?   Yes, they do. Most sharks have hundreds, sometimes even thousands, of sharp teeth. These are arranged in rows of four or more. They fit quite loosely in the jaw. When the front ones break off or fall out, spare teeth move forwards from the rows behind: Sharks get a new set of teeth every two weeks. In 10 years, a Tiger may lose as many as 24,000 teeth!   That's lots of teeth! What kind of food do sharks eat?   Most sharks feed on small fish, and they keep the oceans healthy by eating sick and injured fish. However, hungry sharks will eat almost anything, including smaller sharks and even rubbish. Inside one Tiger shark which was found, there was a tin can, a bicycle tyre , a leather wallet and an alarm clock!   And how do sharks find their food, doctor?   A shark's sense of smell is excellent. It will follow the smell of blood across thousands of metres of ocean. They also see well, and they have good hearing. Sharks can feel movement in water very easily too, and it is possible for them to feel a fish moving as far as 30 m away. Most types of sharks are   _  .
dangerous killers not dangerous afraid of people found inJapan