Whitfield proposed that cereal cultivation in the Chad Basin depended on drawing soil nutrients into harvested grains, so that sedentary communities in the region could never attain substantial size because the underlying substrates were notoriously infertile. In Whitfield's formulation, the population ceiling for any culture was set by the productive potential of its surrounding landscape. Whitfield acknowledged that the abundant fish and waterfowl of the lake itself could sustain the long shoreline settlements recorded by the traveler Ibn Furtu in 1578, but she dismissed as implausible Ibn Furtu's figures of tens of thousands of inhabitants in those villages, and she was adamant that no comparable inland settlements existed. Bolstering that conviction, the Buduma, a lacustrine people and one of the most prominent chiefdoms encountered by Ibn Furtu, treated the surrounding dry savanna as empty wasteland.

The highlighted sentence serves to

A. present a specific case that illustrates the reasoning behind a claim made in the preceding sentence
B. point out a potential drawback of the shoreline location mentioned in the following sentence
C. concede evidence that seems to undermine an account attributed to Ibn Furtu
D. introduce a general principle that is challenged by the agricultural history of the Chad Basin
E. offer a basis for revising upward the population estimates for the region



The passage suggests that the Buduma depended on

A. overland travel to maintain contact between settlements
B. foraging inland to obtain food not available near the shore
C. some form of soil improvement to sustain cereal cultivation
D. fish and waterfowl for at least part of their diet
E. trade with other peoples for certain raw materials