Which choice most logically completes the text?
Historian Maeve Campbell analyzed the adoption of water-powered blast furnaces in fourteenth-century European iron smelting. Metallurgical historians traditionally maintained that access to fast-flowing perennial streams was the primary prerequisite for transitioning from hand-bellows bloomeries to water-powered furnaces. Campbell, however, demonstrated that water-driven bellows could successfully produce molten iron only when furnaces sustained temperatures above 1,150°C—a threshold achievable only if the smelted ore had a phosphorus content below 0.3%, as higher phosphorus concentrations increased slag viscosity and choked heat circulation. Furthermore, operating such furnaces was commercially viable only when local charcoal prices were low enough to offset the watermills' substantial construction costs. Consequently, in regions that possessed abundant water power and cheap charcoal but whose ironmasters nevertheless continued using manual bloomeries, Campbell's framework implies that