Answer:
pretty sure it's d not sure also might be b but I think it's d
Wind erosion is the main cause. And since it is the desert that wind can pick up tiny sand rock particles that slowly grind against the rock. Over time the erosion will give a jagged rock the smooth features as if it had been submerged in a river for the roughly same period of time.
55°. If the intersection in the middle is 90°
