Identify the statement that is true about mass extinctions.
Choose one:
A. The mass extinction of dinosaurs occurred at the Cretaceous/Paleogene boundary.
B. The mass extinction of over two-thirds of the species on the Earth was the result of large volcanic eruptions in Hawaii.
C. Mass-extinction events are times in the Earth's history when few species evolve.
D. A mass extinction may happen when a comet or asteroid impact starts a chain of worldwide volcanic eruptions.