We are told in lines 47-49 that the volcanic-eruption theory may explain why the end of the Cretaceous period was marked by a gradual change in sea level. It goes on to explain that fossil records show that several hundred thousand years before the "relatively sudden disappearance of the dinosaurs," the level of the sea gradually fell, which caused many marine organisms to die out (lines50-54). Further, we are told that the movement of diapirs upward toward the Earth's crust and the more cataclysmic extinction of the dinosaurs could have resulted from the "Explosive volcanism that occurred," (lines 54-60).
Thus, answer choice (B) is the correct answer: "It may explain what caused the gradual fall in sea level that occurred for hundreds of thousands of years prior to the more sudden disappearance of the dinosaurs."
Hope that clears things up! Please let us know if you have any other questions.
