It can be inferred from the passage that the seismic-reflection method would be likely to yield an inaccurate physical profile of the subsurface in which of the following circumstances? A. If the speed at which the wave train moved downward changed B. If the receiver were not positioned directly at the wave-train source C. If the rock on one side of a rock interface had similar elastic characteristics to those of the rock on the other side D. If the seismic records obtained for the different sources in a grid were highly similar to each other E. If there were no petroleum deposits beneath the area defined by the grid of wave-train sources