Which structure comes directly below the excretory system

The ancestors of horses possessed feet with five digits. over time, with the development of grasslands, the digits fused and formed hooves. what evolutionary advantage did this transformation serve? a. it allowed them to climb rocky surfaces with ease. b. it allowed them to graze better. c. it enabled them to run faster from predators. d. it let them see clearly through the grasslands. e. it made them taller.