Final answer:
Mary and Louis Leakey discovered the OH7 fossil, designated as Olduvai Hominid No. 7 at Olduvai Gorge in 1960, significantly contributing to human evolutionary research.
Step-by-step explanation:
The scientists who discovered the Olduvai Hominid No. 7 (OH7) fossil were Mary Leakey and Louis Leakey. The answer to the student's question is A) Mary Leakey and Louis Leakey. The OH7 fossil is an important specimen in understanding early human evolution, comprising a partial juvenile skull, hand, and foot bones linked to Homo habilis, demonstrating physical features distinct from australopithecines, such as smaller teeth. This discovery, made at Olduvai Gorge in 1960 by Jonathan and Mary Leakey, was described by Louis Leakey in 1964 and has played a crucial role in the study of human ancestry. The research by the Leakey family has greatly contributed to our knowledge of hominins and the development of bipedalism. Mary Leakey's later discovery of the Laetoli footprints gave further evidence for early hominin bipedalism, supporting the importance of the Leakeys' findings in paleoanthropology.