What molecular clock might be useful to examine the evolutionary relationship between several phyla in the Plant Kingdom?

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.

your answer should be c) enjoy!

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.