What type of terrain is characterized by hills and undulations?

The correct choice, which describes terrain characterized by hills and undulations, is associated with the term "rolling." This term perfectly captures the essence of an area that is not flat but features gentle rises and falls in elevation, creating a series of smooth hills and valleys. Rolling terrain typically provides a more gradual transition between high and low points, offering a more varied landscape compared to completely flat or significantly steep areas.

The other options describe different types of terrain that do not accurately reflect the characteristics of rolling landscapes. "Level" refers to completely flat surfaces without any changes in elevation. "Mountainous" indicates a terrain that is steep and rugged, with significant vertical relief and typically more dramatic elevation changes than what would be described as rolling. Meanwhile, "flat" suggests an absence of any significant elevation changes, which contrasts with the gentle hills and undulations typical of rolling terrain. Thus, the term "rolling" is the most fitting descriptor for the specified attributes of the terrain.