Worldwide there are probably 70 to 100 shark attacks annually resulting in about 5 to 15 d

eaths. We say "probably" because not all shark attacks are reported: our information from Third World countries is especially poor, and in other areas efforts are sometimes made to keep attack quiet for fear of bad publicity. Historically the death rate was much higher than today, but the presence of readily available emergency services and improved medical treatment has greatly reduced the chances of deaths. Actual numbers of shark attacks certainly are going up each decade because of increasing numbers of bathers in the water, but there is no indication that there is any change in the rate of attack. By far the most common shark attacks are "hit and run". These typically occur in the surf zone where swimmers and surfers are the normal targets. The victim seldom sees its attacker and the shark does not return after a single bite or wound. In most instances, these probably are cases of mistaken identity that occur under conditions of poor water visibility and a harsh physical environment. A feeding shark in this habitat must make quick decisions and rapid movements to capture its traditional food items. Sharks might occasionally misinterpret a human for its normal prey(猎物). We suspect that, upon biting, the shark quickly realizes that the human is a foreign object, or that it is too large, and immediately releases the victim and does not return. Some of these attacks could also be related to social behaviors unrelated to feeding, such as dominance behaviors seen in many land animals. Injuries to "hit and run" victims are usually confined to relatively small cuts, often on the leg below the knee, and are seldom life-threatening.

Not all shark attacks are reported because______.

A．bad news tends to be hidden

B．it is too costly to publicize the data

C．some information is just tricky

D．no one likes to collect the statistics