Craig Rogers wassitting on his surfboard, scanning（审视）the distance for his next wave, when his board suddenly stoppedmoving._________(46)"I could have touched

its eye with myelbow（肘部）,"saysCraig. The shark had surfaced so quietly that he hadn't heard a thing.

In his horror andconfusion,he waved his arms and accidentally cut two of his fingers on theshark's teeth.He then slid off the opposite side of his surfboard into thewater.

Then,with Craig inthe water and blood flowing from his fingers,the five-meter-long shark simplyswam away,_______(47)

Although sharks areoften categorized as killers that hunt and eat as many humans as they can, thisis actually inaccurate.Sharks very rarely kill humans.A person has a

greater chance ofbeing struck by lightning or drowning（淹死）in a bath than of being killed by a shark. Only 74 people have beenreported killed by great whites in the last

century.But greatwhite sharks can reach six meters in length and weigh 2,200 kilograms ormore.With frightening jaws that can hold up to

3,000 teeth arrangedin several rows,they could very easily kill and eat a helpless human in thewater.________(48)Shark researchers are trying to comprehend the reasons

that allow people toescape without being eaten.

The most commonexplanation is that great whites don't see well._________(49)There is reason todoubt this,however. Recent information shows that great whites can

actually see verywell. Also,when attacking seals,great whites shoot up to the surface and bitewith great force.When approaching humans,however,_________(50)They soon

discover that humansare not a high一fatmeal."They spit us out because we're too bony,"says AidanMartin,director of Reef Quest Centerfor Shark Research.

Shark researcherslike Martin hypothesize that great whites are actually curious animals thatlike to investigate things.It's possible that they use their bite not only tokill and

eat,but also togather information.Although such an experience is unlucky for people like CraigRogers,when sharks bite surfboards or other objects or people,they are likely

just trying to learnwhat they are._________（50）

A.disappearing intothe water below.

B.Why isit,then,that most people survive attacks by great whites?

C.they most oftenmove in slowly and bite less hard.

D.There is reason todoubt that great whites see well enough to attack humans.

E.It has beenthought that they mistake people for the seals or sea lions which make up alarge part of their diet.