According to paragraph 2, what is problematic about some scientists' focus on dinosaur extinction? A. Dinosaurs became extinct so long ago that no theory about their disappearance can be proven scientifically. B. Dinosaurs were not the only organisms that went extinct at the end of the Cretaceous period. C. More marine organisms went extinct during the Cretaceous than did dinosaur species. D. It is more important to understand how plankton and other marine organisms came to thrive during the Cretaceous period.