Final Answer:
Eadweard Muybridge's 1878 photos proved that when this animal runs, all 4 feet are off the ground at one point: a) Horse.
Step-by-step explanation:
Eadweard Muybridge conducted groundbreaking photographic experiments in 1878 to settle the debate on whether all four feet of a horse leave the ground simultaneously during a gallop. Using a series of cameras triggered by tripwires, Muybridge captured a sequence of photographs showing a horse named Sallie Gardner in motion. These photographs, known as "Sallie Gardner at a Gallop," indeed proved that at a certain phase of the gallop, all four of the horse's feet are off the ground simultaneously. Muybridge's work not only settled the debate about horse locomotion but also laid the foundation for motion picture technology.
Option A is the answer.