Answer:d
Explanation: because it encompasses all other levels if you see
I have just taken the test, and the answer is in fact B.
251 million years ago, the Permian extinction occurred. It is the widest and most massive extinction that wiped out 85-90% of marine species and 70% of land vertebrates at that time. There were recorded low oxygen levels in deep and shallow oceans, extreme shift in the carbon cycle, massive eruption of a basal salt volcano in Siberia and the consecutive global warming that occurred evidently ended early prehistoric life.
