How Did the Production of Oxygen by Ancient Photosynthetic Microbes

How did the production of oxygen by ancient photosynthetic microbes change the course of evolution on Earth? (Select all that apply)

A) Oxygen gas combined with UV light in the stratosphere to produce an ozone layer that shields Earth from the sun's excess UV rays.
B) The presence of oxygen gas allowed for evolution of aerobic respiration.
C) Oxygen is a greenhouse gas, which caused global warming to overcome the Ice Age and promote the survival of many organisms.
D) Oxygen is toxic to the ancient anaerobic microbes, killing them off to prevent over-population of the planet.