The correct option is A True
Oribi is a small antelope. They feed mostly on the tender grass. The older grass is unpalatable to them. The larger herbivores such as wild buffaloes can eat this grass. They also trample most of them during migration, allowing new smaller grass to grow. Disappearance of big herbivores led to the growth large, stemmy grass that could not support the oribi, causing its disappearance.