Which climate conditions most likely produce a landscape with rounded hills?

Rounded hills are a feature mainly in arid and semi-arid climate regions. This due to the fact that the wind has more of an influence in the erosion process cause the soil is not protected by a layer of vegetation, or the vegetation is very scarce. The wind erodes the hill tops the most as they are the most exposed to them, and has a tendency to flatten them, so the hill slowly over time takes a rounded shape.

The geographic feature in the westernmost corner of kenya is answer: the great rift vally

Why the planet stays in orbit is because of inertia (object stays in motion until a force changes it’s motion) also the atmosphere and gravity!