听力原文： Most people picture sharks as huge, powerful, frightening animals that eat meat, ready at any moment to use their sharp teeth to attack careless swimmers without provocation. There are numerous wrong opinions, however, in this conception of sharks.
First of all, there are about 350 species of shark, and not all of them are large. They range in size from the dwarf shark, which can be only 6 inches long and can be held in the palm of the hand, to the whale shark, which can be more than 55 feet long.
A second wrong opinion concerns the number and typo of teeth, which can vary tremendously among different species of shark. A shark can have from one to seven sets of teeth at the same time, and some types of shark can have sever al hundred teeth in each jaw. It is true that the fierce and predatory species do possess extremely sharp and brutal teeth used to rip prey apart; many other types of shark, however, have teeth more adapted to grabbing and holding than to cut ting and slashing.
Finally, not all sharks are frightening animals ready to strike out at humans. In fact, only 12 of the 350 species of shark have been known to attack humans, and a shark needs to be provoked in order to attack. The types of shark that have the worst record with humans are the tiger shark, the bull shark and the great white shark. However, for most species of shark, even some of the largest types, there are no known instances of attacks on humans.
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A. Categorizing the different kinds of sharks.
B. Warning humans of the dangers posed by sharks.
C. Describing the characteristics of shark teeth.
D. Clearing up some misconceptions about sharks.