托福综合写作满分作文：
氟自来水(adding fluoride in public water)
reading
在自来水中加氟的好处
1.防止蛀牙
2.杀死细菌
3.对骨骼有好处(decrease bone diseases)
lecture
反驳
1.自来水并不会留在口中，对防止蛀牙没有帮助
2.氟会与输水管(water pipe)中的化学物质反应，产生有毒物质，其危害大于细菌
3.过量的氟会使骨骼变脆
托福综合写作满分作文例文：
The speaker refutes the reading's argument about the benefits of adding fluoride to pipe water by providing contradictory evidence about
pipe water's fluoride's effectiveness in preventing cavities in teeth, killing bacteria, and decreasing bone diseases.
Firstly, the speaker points out that the short contact of fluoride with teeth will not enable the fluoride to prevent cavities, as the reading argues. Instead, the water will pass the mouth and teeth quickly and go directly to the stomach.
Another argument raised in the lecture is that fluoride could undergo chemical reactions with heavy metals in the pipe, such as lead. This will create toxic substances which will pose serious health threat. In this way fluoride could be even more deadly than bacteria. Although the fluoride, as the reading says, will kill some bacteria, the cure here is worse than the disease.
In the end, the speaker maintains that overdose of fluoride will backfire to human bones. Although the reading illustrates that fluoride will improve bone strength, the lecture says overdose will cause serious damage to human bones.