题目

Have you ever wondered how a turtle got its shell? You're not the only one. Paleontologists (古生物学者) have long been confused by the question. But a recently found turtle fossil (化石), the oldest on record, may hold the answer. Researchers report in Nature that the fossil shows shells evolved（进化）as an extension of turtles' backbones and ribs (肋骨). “The discovery opens a new chapter in the study of the origins and early history of these fascinating reptiles (爬行动物),” says paleontologist Robert Reisz of the University of Toronto. Scientists have been in甲地（40°N，20°W），乙地（40°S，120°E），甲地位于乙地的A、东北方 B、西南方 C、东南方 D、西北方