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 corn, and about
as many attack wheat. The results of unchecked plant disease are all too obvious
in countries which 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 which are now amply fed by their agricultural products there
could soon be critical 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 a 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 which 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 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 from9 its lack of tolerance. The symptoms shown may cause
an error in diagnosis10, so that treatment may be directed toward bacteria which
could be the result of a susceptibility caused by a primary virus
infection.
单选题
How many diseases are known to attack wheat?
A. Around 30,000.
B. Around 140.
C. Around 29,960.
D. Around 40.
【正确答案】
D
【答案解析】[解析] 细节题。根据数字回到原文定位第一段。30,000种是总的数字，40种是针对玉米，但剩下的29,960种并不都是针对小麦的，所以A、B、C三项都不对。about as many的意思是“大约和……的数目一样”，是指大约与玉米疾病的数量相同，所以应选D。
单选题
According to this passage, which of the following would a plant disease
result in if left unchecked?