D) the embankment
The story begins with the turtle walking over grass, which it does in an unencumbered manner. Even though what is described is a gradual sort of trudging by how the turtle moves itself by slowly “boosting and dragging his shell along,” the turtle trampled through the grass “leaving a beaten trail behind him.” It is when the turtle emerges from the grass and comes to an embankment that there are descriptions of how he is challenged in the climb. However, he was able to overcome this first obstacle.