阅读理解
Although shark attacks can seem vicious and brutal, it''s important to remember that sharks aren''t evil creatures constantly on the lookout for humans to attack. They are animals obeying their instincts, like all other animals. Sharks are designed to hunt and eat large amounts of meat. A shark''s diet consists of other sea creatures — mainly fish, sea turtles, sea lions, and seals. Humans are not on the menu. In fact, humans don''t provide enough high-fat meat for sharks, which need a lot of energy to power their large, muscular bodies.
So why do they attack us? In the majority of recorded attacks, the shark bites the victim, hangs on for a few seconds (possibly dragging the victim through the water or under the surface), and then lets go. The shark is simply mistaking a human for something it usually eats. Once the shark gets a taste, it realizes that this isn''t its usual food, and it lets go.
The shark''s confusion is easier to understand once we start to look at things from the shark''s point of view. Many attack victims are surfers. A shark swimming below sees a roughly oval shape with arms and legs dangling off, paddling along. This bears a close resemblance to a sea lion (the main prey of great white sharks) or a sea turtle (a common food for tiger sharks).
Attacks have also frequently occurred when humans were spear fishing in ocean waters. Sharks are attracted to the signs given off by dying fish — the smell of blood in the water and the electrical impulses given off as the fish struggles. Sharks detect these signals with their ampullae of Lorenzini, a set of "detectors" under the skin on a shark''s snout (嘴). Once a shark arrives on the scene, it may become agitated and aggressive.
There are cases in which sharks seem to attack out of aggression, rather than hunger. Very little is known about shark behavior, but it is believed that some species, including great whites, display dominance behavior over other sharks. This behavior can take the form of "punching" with the snout, or bites that don''t do much damage to the tough skin of a shark. Unfortunately, when a shark makes a dominance display toward a human, these "gentle" bites can still cause horrendous damage.
Sometimes, the cause of a shark attack is the shark is responding to human aggression. Nurse sharks, for example, are generally placid fish that lie still along the bottom of the ocean floor. For some reason, this makes some divers think that it''s a good idea to pull their tails. Irritated nurse sharks have taught several divers to keep their hands to themselves.
In the next section, we''ll go through a moment-by-moment breakdown of a shark attack.
单选题
What does the author think of the sharks'' attack upon human beings?