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It is a question that has long puzzled scientists—exactly why are tigers orange? One might think it makes them more obvious—particularly against a leafy green forest background. William Blake summed it up in his famous poem known by generations of schoolchildren£º“Tyger, tyger, burning bright. In the forest of the night.” But now the answer is at hand.

While obvious to us, computer simulations (Ä£Äâ) of what the big cats look to the main animals they hunt for, deer, show a different picture. Humans with normal colour vision, can see red, blue and green colours. But deer can only pick up blue and green light; they are effectively colour­blind to the colour red, like some humans. It means the tigers' orange colouration looks green to them, allowing them to mix perfectly into the background, new research claims.

Dr John Fennell at the University of Bristol and colleagues said that they used computers to estimate how noticeable a given animal was. They did this by using images of the environment in which the animal lives, and then creating images to see whether the camouflage helps the animal to mix in.

Dr Fennell writes that by simulating what the world looks like to animals who are “two­colour vision”—someone who cannot discover the difference between red and green—“we also identify the most suitable colours for hiding and visibility”£®

Dr Fennell writes in the Royal Society Journal Inter Face£º“Considering the coat of a tiger, it has fur that appears orange to a three­colour vision observer rather than some shade of green, though the latter should be more appropriate colour for an attack hunter in forests. However, when viewed as a two­colour vision observer, the tiger's colour is very effective.”

The question then arises as to why tigers don't grow green coats. Dr Fennell and colleagues write that mammals (²¸È鶯Îï) are not able to produce green fur. To do so would “require a significant change to mammalian biochemistry”. There is only one mammal known to have green fur but this is achieved through what might be considered as, well, cheating, not exactly real.

1£®Why does the author mention the poem in Paragaph 1?

A£®To arouse readers' interest in poems.

B£®To show the author's respect to the poet.

C£®To answer the question of the colour of the tiger.

D£®To stress the noticeable colour of the tiger to us.

2£®What colour is non­existent in the eyes of deer?

A£®Black.  B£®Red.

C£®Blue.  D£®Green.

3£®What does the underlined word “camouflage” mean in Paragraph 3?

A£®The cover of something.

B£®The images of something.

C£®The way of hiding something.

D£®The way of hunting for something.

4£®What can be inferred from the last paragraph?

A£®The colour of tigers sometimes cheats people.

B£®Getting green may prevent tigers from being extinct.

C£®There are no mammals with real green fur in the world.

D£®The tigers' fur will probably evolve into green in the future.