Natureisfullofcolor,fromrainbowsandrosestobutterflyw...

问题详情：

    Nature is full of color, from rainbows and roses to butterfly wings and peacock tails. Even the fruits and vegetables you eat have different colors: blue blueberries, red strawberries, green broccoli, and orange carrots.

    Plant and animals often use color to attract attention. The substances responsible for these colors belong to a class of chemical called antioxidants(抗氧化物). Plants make antioxidant to protect themselves from the sun's ultraviolet(紫外线)light.

    Ultraviolet light causes chemicals called free radicals(自由基)to form within plant cells. They can destroy parts of plant. Free radicals also have damaging effects on human beings. Some of these effects like wrinkled skin can be seen. The damage is caused by the free radicals attacking cells in our bodies. Certain cancers and heart disease are linked to free radicals.

    Our bodies have natural defences for fighting off free radicals. While we are young, our defences are pretty strong. However, they get weaker as we get older. The body’s built-in defences can only go so far without extra help.

    The key to fighting free radicals with fruits and vegetables is to mix and match colors. It’s like sunscreen(防晒霜)for the inside of your body. Go for a range of very bright colors. Colorful foods contain hundreds of healthy chemicals not found anywhere else.

    Research into how chemicals in blueberries affect the brain's function in rats suggests that these chemicals may help our own brains work more efficiently.

    Don't just blame the sun. Ultraviolet light isn't the only source of free radicals. If you breathe polluted air such as smog, automobile exhaust(废气), or wasted gas from a factory, you take in chemicals that also cause such damage. And, the body itself produces free radicals as it processes food.

29. Which of the following NOT true?

   A．Antioxidants are responsible for plant colors.

   B．Plants use color to attract attention.

   C．Antioxidants help free radicals to attack plants.

   D．Antioxidants can protect plants from ultraviolet light.

30. In which order do the following facts occur?

a kled skin can be seen

b aviolet light causes free radicals to form

c radicals damage cells in our bodies

d sun gives out ultraviolet light

   A．a,b,c,d                            B．d,b,a,c

   C．c,a,d,b                            D．d,b,c,a

31. We need extra help for fighting off free radicals from fruits and vegetables because ____.

   A．our defences get weaker as we get older

   B．our bodies’ defences are not natural

   C．we are too young to defend ourselves

   D．our bodies’ built-in defences can only go away

32. Which of the following can NOT cause free radicals to form?

   A．Ultraviolet light from the sun         B．Colorful food

   C．Polluted air                       D．The body itself

【回答】

CDAB

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