to give nonnative plants a chance to colonize the region to prevent the spread of pests that cause damage to plants to replace matured plants with saplings of the same species to rid the forest floor of accumulated deadwood and brush
I gave my students this multiple choice question: 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?

Only one answer is correct among these 4 choices:
- to give nonnative plants a chance to colonize the region
- to prevent the spread of pests that cause damage to plants
- to replace matured plants with saplings of the same species
- to rid the forest floor of accumulated deadwood and brush

Could you tell me which one is correct?

to rid the forest floor of accumulated deadwood and brush