Two paleontologists, Dr Tyson and Dr. Rees, disagree over the interpretation of certain footprints that were left among other footprints in hardened volcanic ash at site G. Dr. Tyson claims they are clearly early hominid footprints since they show human characteristics: a squarish heel and a big toe immediately adjacent to the next toe. However, since the footprints indicate that if hominids made those prints they would have had to walk in an unexpected cross-stepping manner, by placing the left foot to the right of the right foot. Dr. Rees rejects Dr. Tyson’s conclusion.

The disagreement between the two paleontologists is over which one of the following?

Dr. Tyson thinks that the evidence shows the footprints belong to early hominids due to the shape of the footprints, while Dr. Rees believes they can't belong to early hominids because of the walking pattern. Sounds like they're disagreeing over interpretations of different aspects of the evidence.

(A) the relative significance of various aspects of the evidence Bingo
(B) the assumption that early hominid footprints are distinguishable from other footprints Clearly they agree with that, or this disagreement wouldn't happen to begin with
(C) the possibility of using the evidence of footprints to determine the gait of the creature that made those footprints The gait has been determined and is the evidence that Dr. Rees is using, so this is not a point of dissention
(D) the assumption that evidence from one paleontologic site is enough to support a conclusion They're both drawing conclusions, neither one is arguing that no conclusion can be drawn
(E) the likelihood that early hominids would have walked upright on two feet Dr. Rees didn't say anything about this possibility

Which one of the following, if true, most seriously undermines Dr. Tyson’s conclusion?

(A) The foot prints showing human characteristics were clearly those of at least two distinct individuals. This would strengthen Dr. Tyson's conclusion by weakening Dr. Rees's, because it would open the possibility of the strange pattern of footprints being caused by two people walking in a particular fashion, causing the overlap of footprints
(B) Certain species of bears had feet very like human feet, except that the outside toe on each foot was the biggest toe and the innermost toe was the smallest toe. This would explain the "cross-stepping pattern" - because the bear's feet look the same as a human's, except they're essentially reversed. So the footprint from the left foot would look like the right foot, and vice versa. This strengthen's Dr. Rees's position, by giving a reason to believe the footprints might belong to the bear, and thereby weakens Dr. Tyson's conclusion.
(C) Footprints shaped like a human’s that do not show a cross-stepping pattern exist at site M, which is a mile away from site G, and the two sets of footprints are contemporaneous. Strengthen's Dr. Tyson's argument by showing that the cross-stepping pattern might be an anomaly
(D) When the moist volcanic ash became sealed under additional layers of ash before hardening, some details of some of the footprints were erased. I originally answered this by POE until I started typing this post and realized that B is a much better answer. This doesn't really affect either argument, since both conclusions are being made from the same set of prints.
(E) Most of the other footprints at site G were of animals with hooves. Totally irrelevant.