There are nearly 400 different types of sharks, but only about 30 types have even been reported as attacking human beings.
The chances of being attacked by a shark are very small compared to other dangers. Many more people drown（溺死）in the ocean every year than are bitten by sharks. The low number of attacks that happen every year proves that sharks do not feed on humans if they have the choice. There are three types of shark attacks. The main one is known as a ‘hit and run’. The shark attacks because it thinks you are a fish, but when it tastes a human it decides not to eat you. The second type is called a ‘bump and bite’. The shark bumps you to find out if you are fit to be eaten and then bites you if it thinks you are. The third type is called a ‘sneak’. When attacking in this way, the shark waits for you to swim by and attacks you suddenly. The latter（后者的）two types of attack are more likely to be deadly for humans.
However, your chances of being attacked by a shark can be reduced if you follow the advice below.
Do not swim in the dark. Sharks can still see you but you cannot see them.
Do not swim if you are cut or if you have a fresh wound. Sharks can smell blood over a long distance.
Do not wear bright clothing or jewellery because sharks are attracted to colours and shiny objects.
Try and stay in groups, as sharks usually avoid large numbers of people.
Don’t be frightened（受惊吓）by sharks as there is 30 times greater chance of being hit by lightning than being attacked by a shark.
Are there only 30 types of sharks in the world?
Are the chances of being attacked by a shark small or big compared to other dangers?
What are the two deadly shark attacks called?
Why should you try and stay in groups to avoid the shark attack?
What does the writer mainly tell us in the passage?