课时梯级训练(20) UNIT 5 Section Ⅳ Writing（Word练习）-【优化指导】2023-2024学年新教材高中英语选择性必修第一册（人教版2019）

课时梯级训练(二十) 　Section Ⅳ　Writing Ⅰ.阅读理解 (2022·盐城高二检测)Greenhouse gas emissions(排放) would rise if all farms in England and Wales went organic.Though the emissions of each farm would go down，much more food would have to be imported，as the amount they would produce would decrease greatly. “The key message from my perspective is that you can't really have your cake and eat it，”says Laurence Smith，now at the Royal Agricultural University in the UK，who was part of the team that ran the numbers.Smith is a supporter of organic farming and says“there are a lot of merits of the organic approach，”but his analysis shows that organic farming has downsides too. Farming and changes in land use，such as cutting down forests，are responsible for a third of all greenhouse gas emissions.That means reducing farming emissions and the land needed for farming is required to limit further global warming. Smith and his colleagues found that emissions per unit of food are，on average，20 percent lower for organic crops and 4 percent lower for organic animal products.However，organic harvests per hectare(公顷) are also lower on average.For wheat and barley，for instance，harvests are just half of those of conventional farms.This means 1.5 times as much land would be needed to grow the same amount of these foods. The estimated increase in emissions varies greatly，depending on where the extra farmland comes from.If only half comes from turning grassland into farms，the increase could be as low as 20 percent.If grassland that would otherwise have been reforested is turned into farmland，emissions could nearly double. This doesn't necessarily mean people should stop eating organic produce，says Smith.People might choose organic food for other reasons，such as to reduce their pesticide exposure(though contrary to popular belief，organic farmers do use pesticides) or for the sake of wildlife. Going 100 percent organic could also harm global biodiversity.The extra land used for farming would mean the land availabl