托福阅读材料：鲨鱼是色盲？

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　　Wearing a light blue wetsuit that matches the colour of the sea will make you less likely to become the victim of a shark attack, according to researchers. Sharks are completely colour blind and only see things clearly if they are mostly light or dark, scientists have claimed. In a breakthrough that could prove hugely beneficial to divers navigating shark-filled waters, scientists found that the predator - like dolphins, seals and whales - is unable to distinguish between colours. Costumes or wetsuits that camouflage swimmers' bodies in the sea water are less likely to draw a shark's attention than ones with bright, solid colours than emphasise their outline.

　　Professor Nathan Hart, from the University of Western Australia, said: 'It’s the high contrast against the water rather than the colour itself which is probably attractive to sharks. 'So you should wear perhaps more muted colours or colours that match the background in the water better.' The researchers examined the eyes of dead sharks and found they had only one type of photoreceptor in the retina, indicating they could only see in monochrome.

　　The U.S. Navy has conducted tests that suggested sharks were able to see yellow most clearly. The tests had been to see what would be the best colour for the lifejackets that pilots wear in case they have to eject and splash down in the ocean. Professor Hart said it was more the high contrast of yellow, not the colour itself, that would increase the visibility for sharks. He said: 'It may be possible to design swimming attire and surf craft that have a lower visual contrast to sharks and are therefore less attractive to them.' The study by researchers at the University of Western Australia and the University of Queensland, is to be published in the German nature journal Natur wissenschaften (Science of Nature).