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听力原文： Scientists have discovered that plants themselves produce many poisonous chemicals for defense against insects. But insects have developed ways of dealing with them. Guess how many years have the insects been eating plants. The number itself will scare you. In fact, insects have been eating plants for as many as 250 million years. Now insects are using these same mechanisms to deal with man-made poisons—insecticides. This is why resistance of insects to insecticides has developed so rapidly.
What should be done？ Scientists studying the problem suggest that farmers use less insecticides. At the moment, farmers regularly spray crops as a precaution against problems that are caused by large numbers of pests. They should, instead, spray only where pests have actually been seen. Secondly, farmers could use a combination of two or three insecticides at once. To survive, the insects would need to become resistant to two or more insecticides at the same time.
The most surprising suggestion, perhaps, is that at certain times of the year, farmers should actually try to attract new insects onto the crops they are trying to protect. The new insects will mate with those which survived from a certain kind of insecticide and will lessen the latter's resistance to it.
Scientists hope that these and other measures will postpone the day when farmers and scientists will have to stand by while new super-bugs which may be resistant to all poisons invade our farms and devour our crops.
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A．He should try a better and convenient way.B．He should give up looking for the book.C
清朝敕封西藏喇嘛教首领的意义在于()。
Section A
Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and the questions will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked A, B, C and D, and decide which is the best answer.
(12)
Sir Humphrey Gilbert led the first English settlement efforts but failed. Gilbert's half brother Sir Walter Raleigh continued his work. Raleigh sent a number of ships to explore the east coast of North America. He called the land Virginia to honor England's unmarried Queen Elizabeth.
In 1585 .about one-hundred men settled on Roanoke Island, off the coast of the present day state of North Carolina. These. settlers returned to England a year later. Another group went there the next year. This group included many women and children. But the supply ships Raleigh sent to the colony failed to arrive. When help got there in 1590, none of the settlers could be found.
History experts still are not sure what happened. Some research suggests that at least some of the settlers became part of the Indian tribe that lived iii the area.
One reason for the delay in getting supplies to Roanoke was the attack of the Spanish Navy against England in 1588. King Phillip of Spain had decided to invade England. But the small English ships combined with a fierce storm defeated the huge Spanish fleet. As a result, Spain was no longer able to block English exploration.
England discovered that supporting colonies so far away was extremely costly. So Queen Elizabeth took no more action to do this. It was not until after her death in 1603 that England began serious efforts to start colonies in America.
(30)
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