Answer: c. Slows down or hits an obstacle
Step-by-step explanation:
Wind moves either in a slow or fast pattern depending on the velocity by which they are propelled by, when they move with sand grain they deposit the sand grain either when they slow down or hit an object. When they slow down it relates that the velocity with which they kicked off with has started depretiating hence the force with which they travel with begins to reduce or reduce instantly. Secondly when they hit an obstacle they can't move again because the obstacle has a greater force than them. These are occasions when wind carry a sand grain can deposit it.