阅读材料
It’s not clear that cloud seeding is all that effective and there are reasons to question each of the arguments you just read. First, it may be true that under laboratory conditions silver iodide creates snow instead of hail. However, in real life, silver iodide can actually prevent any precipitation at all from forming in the cloud, snow, rain or hail. This is a bad thing. Because if you seed all the clouds in areas where it doesn’t rain very often, you ran the risk of causing a drought. In this case the crops simply get damaged for a different reason: lack of water.Second, it's not clear that positive result of cloud seeding in Asia can be repeated in the United States. The reason is that cloud seeding in Asia was tried in urban areas, in cities. And cities tend to have a high level of air pollution, from car, factory, etc. Surprisingly, pollution particles can create favorable conditions for cloud seeding because they interact with clouds and seeding chemicals. Such favorable conditions for cloud seeding may not occur in an unpolluted area. This means that the cloud seeding method that works in polluted cities may not work in unpolluted farming regions in the United States.Third, the local study mentioned in the passage isn’t very convincing either. That’s because the study found that hail damage decreased not just in the area where the cloud seeding actually took place, but also in many of the neighboring areas to the east, south and north of the area. So the fact that the whole region was experiencing a reduce number of hail storms that particular year makes it more likely that this was a result of natural variation in local weather, and has nothing to do with cloud seeding.
Summarize the points made in the lecture, being sure to explain how they respond to the specific points made in the reading passage.
The author discussed that although hail makes crops suffer a lot, there has always been a method called cloud seeding which can protect crops from this disaster. He listed three facts supporting this approach. However, the speaker holds a contradictory view that all these three ways are not reliable. First, the writer proposes that laboratory experiments has already proved that cloud seeding is effective in eliminating hail. But the professor points out that although the hail can be turned into rain and snow in experimental movement, but it is also possible that hail, snow and rain can be all prevented by cloud seeding. Consequently, it will cause drought. Crops will still be damaged as a result of lack of water. The writer’s first argument is refuted. Second, the passage indicates that cloud seeding has an Asia evidence. To render this disproof, the lecturer reveals that this successful application in Asia probably will not get a similar outcome in America. High air pollution offers favorable conditions for cloud seeding process because those polluted air can interact with cloud and seeding chemicals. So this method which can be used in cities area may not be effective in unpolluted farming area. The second idea in the passage is also retorted. Third, the essay says that local studies in central United States also attain a satisfying result. Nevertheless, the speaker rebuts this idea. He thinks it unconvincing because hail damage in whole America not only decreases just in central of America, but also in the east, south and north part of country. So it is hard to say cloud seeding is the exact factor causes all those good things. Natural variation and local weather can also contribute to the elimination of hail disaster. This overturns the writer’s concept. (294 words)
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