The Most Dramatic Mass Extinctions of Organisms Are Thought to Have

The most dramatic mass extinctions of organisms are thought to have taken place at the end of the Permian period. What factor(s) likely contributed to these extinctions?

A) Volcanic eruption
B) Glaciers
C) Decrease in the oxygen content of the atmosphere
D) Increase in the amount of sunlight penetrating the atmosphere
E) All of the above