When Looking at the Atmospheric CO₂ Concentrations Collected from Ice

When looking at the atmospheric CO₂ concentrations collected from ice core layers over the last 500,000 years, what does one see?

A) an ever-increasing level of CO₂ from 500,000 years before the present (BP) to today
B) an ever-decreasing level of CO₂ from 500,000 years BP until 150,000 years BP and then a steady rise until today
C) a varying level of CO₂ from 500,000 years BP to today
D) no change in the level of CO₂ from 500,000 years BP until just recently (the last 100 years of human history)