A、A shark attacks a person for no reason. B、A shark attacks a person every time it sees one. C、A shark attacks a person only if

Most people picture sharks as huge, powerful, frightening predators, ready at any moment to use their sharp teeth to attack unwary swimmers for no reason. [29] This idea of sharks, however, contains many misconceptions.
    First, there are about 350 species of shark, and not all of them are large.
    A second misconception concerns the number and type of teeth, which can vary tremendously among the different species of shark. A shark can have from one to seven sets of teeth at the same time, and some types of sharks 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. [30] Many other types of sharks, however, have teeth more adapted for grabbing and holding than for cutting and slashing.
    Finally, not all sharks are predatory animals ready to strike at humans without warning. In fact, [31] 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.