sentence2_structure: A fewer predators<>is<>most likely to cause the number of rabbits$$$A fewer predators<>to cause<>the number of rabbits$$$rabbits<>living<>in an area<>to increase$$$the number of rabbits<>to increase<>
sentence1: With the decline of such natural predators as wolves and tigers, the number of wild boars has increased, causing problems for farmers in some areas.
sentence2: A fewer predators is most likely to cause the number of rabbits living in an area to increase.
question: Which factor is most likely to cause the number of rabbits living in an area to increase?