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  3. The problem of the American robin is an example of the hidden dangers involved in the use of insecticides. Elm trees in the Unit

The problem of the American robin is an example of the hidden dangers involved in the use of insecticides. Elm trees in the Unit

admin2010-04-24  77
问题     The problem of the American robin is an example of the hidden dangers involved in the use of insecticides. Elm trees in the United States, like those in Europe, are being attacked by Dutch elm disease. This fungal disease is spread by the elm bark beetle.
     American scientists have attacked the disease by attacking the carrier. They have treated the trees with a chemical which kills the beetles. But the substance they use sticks to the leaves of the trees. These leaves are a basic food of a certain type of earthworm which is itself not affected by the insecticide. The worm can store up huge quantities of this poison in their systems. The robin eats these worms and is thus being poisoned by its normal food. The bird is already in danger of dying out in some areas.
     It is sometimes difficult to foresee side effects like these, which is why many people object to the use of chemical sprays. They fear that man may be poisoning himself in the same way as he has poisoned the American robin and other higher organisms at the top of food chains.  
The main idea of the passage is that
选项 A、the side effects of insecticides may be serious and hard to predict
B、the robin is near extinction in some parts of the world
C、American scientists have succeeded treating Dutch elm disease
D、elm trees must be protected against beetles
答案A
解析
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