Dr. Tyson believes that the shape of the footprints is most significant, whereas Dr. Rees believes that the relevant placement of the footprints is most significant. (A) describes the disagreement that leads to the doctors' differing conclusions.

Both paleontologists claim that they can distinguish whether the footprints were made by a hominid or another animal—they simply disagree on the answer. But making this claim shows us that both paleontologists agree that hominid footprints are distinguishable.

Dr. Rees is the only one who determines the creature's gait from its footprints, but Dr. Tyson never disagrees that this is possible. Dr. Tyson just focuses on the footprints' shape rather than the creature's gait.

Both paleontologists draw a conclusion just based on one paleontologic site, which tells us that both paleontologists agree that evidence from one site is enough to support a conclusion. The conclusions they draw are just different: Dr. Tyson thinks the footprints were from a hominid, and Dr. Rees thinks they were not.

Neither paleontologist discusses how likely it is that early hominids would have walked upright on two feet. Because neither paleontologist expresses an opinion, we can't say whether they agree or disagree on this point.