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Even in fresh water sharks hunt and kill. The Thresher shark, capable of lifting a small boat out of the water, has been sighted a mile inland on the Fowey River in Corn wall. Killer sharks swim rivers to reach Lake Nicaragua in Central America; they average one human victim each year.
Sewage and garbage attract sharks inland. When floods carry garbage to the rivers they provide a rich diet which sometimes stimulates an epidemic of shark attacks. Warm water generally provides shark food, and a rich diet inflames the shark’s aggression.
In British waters sharks usually swim peacefully between ten and twenty miles off shore where warm water currents fatten mackerel and pilchards for their food. But the shark is terrifyingly unpredictable. One seaman was severely mauled as far north as Wick in Scotland. Small boats have been attacked in the English Channel, Irish Sea and North Sea.
Most of the legends about sharks are founde
A. They prefer warm water to cold water.
B. They see best in deep water.
C. They are afraid of man.
D. That is where their food is．