Refer to the Graph Showing Variations in Oxygen Levels During

Refer to the graph showing variations in oxygen levels during Earth's history. Which of the following can be concluded from the graph?

A) Increased atmospheric oxygen levels coincided with a decrease in insect size.
B) Multicellularity preceded the evolution of photosynthesis.
C) The first forms of life on Earth did not use oxygen.
D) Overall, atmospheric oxygen levels have decreased over Earth's history.
E) The first flowering plants required giant flying insects for pollination.