Task: Question Answering
Input (English): In some national parks, controlled fires are maintained by firefighters. Which of these is one of the major reasons for using controlled burns to maintain certain ecosystems?  
 (A) to give nonnative plants a chance to colonize the region (B) to prevent the spread of pests that cause damage to plants (C) to replace matured plants with saplings of the same species (D) to rid the forest floor of accumulated deadwood and brush
Output (English): D