What is a gene? what number should replace the letter x in the “seed color” row?

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

What is the cause hearing loss in human being

Diagram of the evolution of land plants?