The stimulus presents two arguments about government subsidies for the agricultural district of Rochelle in the country of Cariana. Alan argues that, since implementing new agricultural techniques is necessary to control the erosion of productive topsoil, and since farmers can't afford to implement these new techniques on their own, agricultural output in Rochelle will "inevitably decline" without subsidies.

Betty responds that the cause of the erosion is recurring floods, which will stop when Cariana finishes a new dam next year. She concludes that Rochelle's total agricultural output will "stabilize at the present level" even if Rochelle doesn't receive subsidies.

Betty states in her premise that the cause of the erosion will be eliminated next year — so starting sometime next year, Rochelle's topsoil will no longer be eroded due to flooding. Her conclusion states that Rochelle's agricultural production will stabilize at the present level. This very specific prediction about the net effect of building the dam requires Betty to assume that between this year and next, when the dam will be completed, there will not be enough erosion of topsoil or other changes that will cause a permanent decline in Rochelle's agricultural production. Betty also assumes that the dam will be completed and not just abandoned.