15．Sharks （鲨鱼） 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 stay on the beach．It will be too late if a shark can swim sixty kilometers an hour to you． There are 30kinds of sharks and 25kinds of them are dangerous．The whale sharks are very big．They can grow to 18meters long，but they are not dangerous to people．The jaws （大白鲨） 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 calm 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． 51．Why do people put nets around some beaches？C A．To keep swimmers running． B．To keep swimmers swimming． C．To keep swimmers safe． D．To keep sharks swimming． 52．B of sharks are dangerous in all kinds of sharks． A．Less than 80% B．More than 80% C．More than 90% D．Less than 20% 53．What are the most dangerous kinds of sharks？A A．The jaws and the tiger sharks． B．The whale sharks and the tiger sharks． C．The jaws and the whale sharks． D．The whale sharks and the blue sharks． 54．What does the underlined word mean in Chinese？A A．安静 B．吵闹 C．沉默 D．任性 55．Which is NOT true according to the passage？C A．It will be late if a shark can swim sixty kilometers an hour to you． B．There are 30kinds of sharks in the sea． C．All sharks must keep swimming to go down in the sea． D．Sharks'teeth can grow out very quickly．
