According to Geological Evidence and Computer Models Based on That

According to geological evidence and computer models based on that evidence,which statement about the concentration of oxygen in our atmosphere is correct?

A) No oxygen was present prior to the Cambrian Era; oxygen levels have uniformly risen since,and today's atmosphere is more oxygen rich than at any time in the Earth's history.
B) Oxygen levels were greatest during the Cambrian Era but have been steadily declining ever since; today's atmosphere is less oxygen rich than at any time in the Earth's history.
C) Oxygen levels have generally risen during the Phanerozoic Era but peaked during the Mesozoic Era (Age of Dinosaurs) and declined sharply in the Early Cenozoic Era.
D) Oxygen levels have generally risen during the Phanerozoic Era but peaked during the Late Paleozoic Era (the time of coal swamp forests) and declined sharply in the Early Mesozoic Era.