A farmer cultivates a different crop in the same field each year for three years. In the fourth year, the farmer grows a leguminous crop and then ploughs it into the soil. The following year, the rotation starts once more. Which microorganisms will have increased by the time the rotation starts again?
- A1, 2 and 3
- B1, 2 and 4
- C1, 3 and 4
- D2, 3 and 4