Sharks   are the most frightening animals in the sea. Sometimes we can see sharks swimming in the sea around Hong Kong. People put nets around some beaches to protect swimmers. When there is a "shark's flag", people must slay on the beach. It will be too late if a shark can swim sixty kilometers an hour to you. There are 30 kinds of sharks and 25 kinds of them are dangerous. The whale sharks are very big. They can grow to 18 meters long, but they are not dangerous to people. The jaws   and the tiger sharks are the most dangerous kinds of sharks. Do you know all sharks must keep swimming, or they will go down? All sharks can feel everything that happens around them. We must keep _ and don't make any noise when a shark is swimming near you. If a shark loses a tooth, a new one will grow out very quickly. So sharks always have many sharp teeth. _   of sharks are dangerous in all kinds of sharks.
Less than 80% More than 80% More than 90% Less than 20%