More than 90% of all mammal species are
a. monotremes.
b. marsupials.
c. placental mammals.
d. domestic animals.

C. Placental mammals

Explanation:

The placentals are the largest group of mammals, totally dominating the class and terrestrial habitats.

Amnium, the fluid that protects the embryo from adhesions and shocks, is installed in the female's uterus for development with the help of a placenta that provides fixation and nutrients.

This breeding method, although producing a smaller number of offspring per pregnancy, has a high success rate, allowing greater chances of survival to offspring.

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.

hello there the answer is d