单选题 Subterranean streams have cut through limestone to form miles of passages and caves such as Kentucky's Mammoth Cave.
【正确答案】 B
【答案解析】[词义辨析] suterranean指“地下的”，与B项的undeground(地下的)同义。secondary“次要的”；unharnessed“未开发的”；miniscule“很小的”。