Deep tillage is even more deleterious to the world' s topsoil supply than previously believed. For example, farmers who till deeply are ten times more likely to lose topsoil to erosion than are farmers who use no-till methods. Results like these make it clear that farmers who now till deeply should strive, by using other topsoil aeration techniques, to incorporate no-till methods instead. The argument depends on assuming which one of the following? ['In deep-tillage farming, the deeper one tills, the greater the susceptibility to topsoil erosion.', 'Topsoil erosion does not make farmers want to till more deeply.', 'The most expensive farming methods employ topsoil aeration techniques other than deep tillage.', 'Tilling by any method other than deep tillage is not a viable option.']