Why Are Assemblages of Fossils Seen in Successive Geological Periods

Why are assemblages of fossils seen in successive geological periods so different?

A) Rapid continental drift has altered the positions of continents such that the strata represent different locations on Earth.
B) Rapid bursts of evolution have occurred due to changes in oxygen concentrations.
C) Mass extinctions and the subsequent rebound of biological diversity have brought about sudden changes in the assemblages.
D) Organisms continue to evolve during periods when fossilization does not occur.
E) Fossil assemblages across successive strata blend into one another,and there are no sharp breaks.