Answer:
A. Species that remained after the extinction were able to radiate, new adaptations arose, and these adaptations produced the diversity seen today.
Explanation:
When species went extinct they also left niches that could be occupied by "new" species; new places to live, places to be filled in the food web and different relationships to be formed. The wide availability of resources made organisms to radiate leading to a "new" diversity of shapes, sizes, and lifestyles.
B. Species that have gone extinct were able to re-evolve from the ancestors that survived the extinction. If you are extinct you are gone forever.
C. Species that remained after the extinction were unable to speciate. Therefore, the number of species on Earth today is lower than the number of species present just before either extinction. The fossil record proves that species have changed over time and the diversity has changed over the history of Earth.
D. Species that remained after the extinction represented all of the lineages that were present before the extinction event. Therefore, extinction did not change the diversity of lineages. Again, the fossil record is evidence that lineages have changed over the history of the Earth.
