could pigs actually fly through decades of crossbreeding animals and perfecting a breed of pig that physically could grow wings and adapt

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.

i think the answer would d

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.