Mammals evolved into larger organisms and began subdividing into various species in the a. mesozoic era c. cenozoic era b. paleozoic era d. devonian era

The answer is C. Cenozoic era. 
It's the era when mammals evolved into larger organisms and began subdividing into various species. Cenozoic is also known as the age of mammals, because it's the mammals that mostly occupied the lands.

I agree with the first answer

It is used to during sexual reproduction between humans