题目解析:
用 Loop 定位到原文:Because the model was originally based on studies of Chicago, its center is labeled ""Loop,"" the term commonly applied to that city's central commercial zone.
原因很明显,有 because 引出原因,不用绕弯,直接出答案。这个新的模式就是基于对芝加哥的研究,因此选 C。A 选项无提及;B 选项的 in transition 在原文由提及,为干扰选项,答非所问,并不是 loop 被使用的原因;D 选项的 returned to zone 也不是原因。