Task: Question Generation
Input (English): Background Paragraph: Because of human activities, there is more carbon dioxide in the atmosphere today than in the past hundreds of thousands of years. Burning fossil fuels and has released great quantities of carbon dioxide into the atmosphere. Cutting forests and clearing land has also increased carbon dioxide into the atmosphere because these activities reduce the number of autotrophic organisms that use up carbon dioxide in photosynthesis. In addition, clearing often involves burning, which releases carbon dioxide that was previously stored in autotrophs. 
Story: Two researchers looked at the human influence on atmospheric carbon dioxide levels. Tim studied a human settlement from 10000 years ago, while Bob studied a present day county. Today's economy in the county revolved around extensive agriculture.
Output (English): Which researcher found that clearing often involves burning?