The best explanation for why the amount of land used for dairying is much smaller than the pasture used for beef cattle is Option B:
"Dairy cows must be kept close to farmhouses, as they require daily milking, and milk must be produced close to consumers, as it is highly perishable."
This option highlights the need for dairy cows to be located near facilities where they can be milked regularly and near consumers due to the perishable nature of milk, which necessitates smaller, more localized operations compared to beef cattle, which can be raised in more extensive pastures away from urban areas.