单选题 . ①Noting that bison herds appear to graze selectively in areas occupied by prairie dog colonies, Coppock hypothesized that the attraction is due to improved forage quality: prairie dogs' own grazing activities alter herbage dynamics, plant species composition, and nutrient cycling. ②The colonies' territory contains relatively little low-quality mature standing herbage and is characterized by communities of plants that are high in crude protein and highly digestible. ③However, such effects are not produced only by prairie dogs. ④Willms showed that sites selectively grazed by cattle had reduced standing dead plant material, altered species composition, and increased soil nitrates, ammonium, and available phosphorus. ⑤In fact, long-term, intensive use by any grazer will cause comparable changes in plant communities.29. The highlighted sentence serves primarily to ______

A、 provide information about the kinds of forage preferred by prairie dogs
B、 refute a particular claim about the forage methods of prairie dogs
C、 specify what makes forage conditions created by prairie dogs appealing to bison
D、 suggest that prairie dogs' activities can cause environmental degradation
E、 identify characteristics that influence prairie dogs' selection of sites to colonize

【正确答案】 C

【答案解析】 C：本题属于功能题，定位句是例子，用于说明土拔鼠具体做了哪些改变使得这片土地能够吸引野牛，因此选项C正确。