托福official36综合写作科技类Integrated Writing范文+题目解析

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.