题型：阅读理解 题类：常考题 难易度：普通
北京顺义区2019届高三上学期英语期末考试试卷
A Colourful Puzzle
People often wear clothing with colours that express something about themselves. A happy person might choose to wear a bright yellow shirt. A swimmer might wear a sea-blue dress.
Animals appear in different colours too, but they don't get to pick what they wear every morning. Scientists have known for a long time about some of the ways animal colouring can be beneficial. They know that some animals' colours attract mates or show who is boss. Other animals' colours blend(融合) in with their environment; thus the animals cannot be seen by their enemies. Still, scientists do not fully understand why blue jays are blue or why rainforest frogs are golden. Now many scientists are working hard to figure out the puzzles of animal colours.
Part of the answer can be found in an animal's habitat, the place where it lives. It turns out that many animals — especially birds, fish, and reptiles — can see more colours than humans can. These creatures notice colours that stand out in their habitat. For example, forests are mostly green, brown, and yellow. For an animal to be seen by others of its species, it would have to be a different colour than its background. That explains why you can find birds of many shades of blue living in forests.
Another piece of the puzzle lies in what an animal eats. Birds often eat things that have chemicals in them called “carotenoids”(类葫萝卜素). These chemicals are what make tomatoes red and bell peppers bright orange or yellow. When birds eat these foods, the carotenoids affect the colour of their feathers. For example, a cardinal's bright red feathers will become lighter or darker depending on how many berries it has found to eat.
Some animals do not have any colour at all — but they are not just white; they are transparent(透明的)! Transparent animals live mostly in the ocean. This amazing wonder of nature came about because the animals needed a way to escape their enemies. They are often slow, defenseless creatures that would have no way of fighting back if larger animals wanted to eat them. Because there are few places to hide in the ocean, these creatures have to hide in plain sight. A good example of this kind of transparent creature is the jellyfish. A jellyfish's body is almost all water, so it is very hard to see it floating in the ocean.
Animals come in all kinds of colours. Their colours are caused by many different factors, and most animals will remain the same colour for their whole lives. Think how lucky we are to get to change our feathers every day!
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