What can you conclude from the fact that more than a billion species have gone extinct during earth's history? a. extinction is a natural part of life on earth b. extinction happens only rarely c. the rate of extinction has increased since humans evolved d. the earths environment is not good at supporting life

the correct choice is i and iv.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.