What happens to oxygen levels when animals are introduced? Why?

Agenetically engineered corn plant is approved for agricultural use. the plant produces pollen that can make its own toxins. these toxins protect the corn plant against pests and no longer require the application of chemical pesticide. what is a likely impact on the farmer of growing such a variety of corn? a- the financial costs for the farmer would be lowered since less crops would be lost to pests. b-the financial costs for the farmer would be lowered since more crops would be lost to pests. c-the farmer may be held responsible for increasing chemical pollution. d-the farmer's expenses for pest control would increase due to an increase in bee population.