What can be a appropriate scale number to start off on the y-axis ? answer this

What did not occur in the proterozoic eon a)the oxygen levels increase greatly in the atmosphere,b)the emergence of the eukarya , c)muti cella’s eukaryotic organisms began to diversify,d)anaerobic bacteria kept thriving with more oxygen

Match the description of each organism to the appropriate category

The third stage of cellular respiration is (2 points)