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结构中含有异丁基的药物是E．
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Diseases of Agricultural Plants
Plants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack com, and about as many attack wheat. The results of unchecked plant diseases are ail too obvious in countries that have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries that are now amply fed by thek agricultural products there could soon be food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world.
Some plants have relative immunity to great many diseases, while others have a susceptibility to them. The tolerance of a particular plant changes as the growing conditions change. A blight may be but a local infection easily controlled; on the other hand it can attack particular plants in a whole region or nation. An example is the blight that killed virtually every chestnut tree in North America. Another is the famous potato blight in Ireland in the last century. As a result of that, it was estimated that one million people died of starvation and related ailments.
Plant pathologists have made remarkable strides in identifying the pathogens of the various diseases. Bacteria may include invade a plant through an infestation of insect parasites carrying the pathogen. A plant can also be inoculated by man. Other diseases might be caused by fungus which attacks the plant in the form. of a mold or smut or rust. Frequently such a primary infection will weaken the plant so that a secondary infection may result from its lack of tolerance. The symptoms shown may cause an error in diagnosis, so that treatment may be directed toward bacteria which could be the result of a susceptibility caused by primary virus infection.
How many diseases are known to attack wheat？
A．Because immigrants miss their native cuisine.B．Because immigrants are fond of cooking
Section B
Directions: This section is to test your ability to understand short conversations. There are 2 recorded conversations in it. After each conversation, there are some recorded questions. The conversations and the questions will be spoken only once. When you hear a question, you should choose the correct answer from the 4 choices marked A, B, C, and D.
听力原文：W: How was the flight, Tony？
M: Difficult. The weather was bad, and we were late getting into San Francisco. I'm sure that most of the passengers weren't happy about the flight!
W: It seems like you travel a lot for work. Do you really like your job？
M: Sure, Lisa. Today was just a bad day.
W: Why do you like it？
M: I like to go places with people, and I like to travel.
W: What's your favorite place？
M: That's a hard question. I like South America. I go to Colombia and Brazil a lot. The people are very nice, and I like the weather there. It's always warm. Of course, I like the United States, too. New York is nice in summer, but I don't like it in winter.
W: Why not？
M: It's cold. I hate cold weather.
W: That's interesting. I love winter. I love ice-skating.
(6)
Section A
Directions: This section is to test your ability to understand short dialogues. There are 5 recorded dialogues in it. After each dialogue, there is a recorded question. The dialogues and the questions will be spoken only once. When you hear a question, you should decide on the correct answer from the 4 choices A , B, C, and D.
听力原文：M: Miss, is there still time for a cup of coffee on this flight？
W: Yes, but you have to drink it fast, because we'll be landing in 10 minutes.
Q: Where did the dialogue most probably take place？
(1)
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