The correct answer is (a) Human control
The explanation: Human control is one of the major advantages of anaerobic fermentation over aerobic composting which can control the liquid and gaseous emissions, which is not the case for aerobic composting. High water content or low water content is irrelevant to this advantage. Also, the ability of re-use of methane by the engineers, in the process is a major advantage. So, in this case production of methane is not very relevant.