Most people picture sharks as huge, powerful, frightening predators, (1)__________________________. But, people may have some wrong ideas on the conception of sharks.First, there are 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.Second, (2)______________________________. A shark can have from one to seven sets of teeth at the same time, and some types of shark can have several hundred teeth in each jaw.It is true that the fierce and predatory species do possess extremely sharp and brutal teeth used to rip their prey apart many other types of shark, however, have teeth more adapted to grabbing and holding than to cutting and slashing. Finally, not all sharks are predatory 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. (3)_________________________________, 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.
ready at any moment use their sharp teeth to attack and swimmers without
the different species of shark very in the number and type of teeth
the type of sharps they have the worse to the humans are the tiger sharp
发表于 2011-4-29 13:41
| 
发表于 2011-4-29 18:38
| 