burnt-up fraction

例句：

1. 1.The scientist analyzed the burnt-up fraction of the sample to determine its chemical composition.
   科学家分析了样品的燃烧后剩余物，以确定其化学成分。
2. 2. The team worked tirelessly to extract the burnt-up fraction from the ash.
   团队努力不懈地从灰烬中提取燃烧后剩余物。
3. 3. The research focused on the burnt-up fraction of the fossil fuels, which could be used as a source of energy.
   研究专注于化石燃料的燃烧后剩余物，这些物质可以作为能源的来源。