6. Significant mass extinctions occurred during which of the following epochs?
O A. Triassic, Permian, and Cretaceous
B. Triassic, Permian, Cretaceous, Pleistocene, Ordovician, and Devonian
O C. Pleistocene, Ordovician, and Triassic
D. Ordovician, Triassic, Jurassic, Silurian, Eocene, and Oligocene