Which is not a hypothesis stated in the text for why the Cambrian explosion occurred? A. The different chemistry in the ocean made it easier for animals to secrete hard shells
B. A super volcano exploded changing the environment and causing change in the animals
C. Oxygen levels reached a level that allowed animals to be more efficient at using aerobic metabolism
D. The emergence of predatory animals that could move around and eat other animals favored animals that could move or protect themselves.