The correct answer is option 1, faulting. Rift valleys and horsts are geological features that are created as a result of faulting in the Earth`s crust. Faulting occurs when there is a break or fracture in the Earth`s crust, and the rocks on one side move relative to the rocks on the other side.

In the case of rift valleys, the Earth`s crust is stretched and pulled apart due to the forces of tension. This stretching causes the crust to crack, and the rocks on either side move away from each other, creating a large depression or valley. These rift valleys are commonly found in areas where tectonic plates are diverging, such as the East African Rift Valley.

On the other hand, horsts are raised blocks of land that form between parallel fault lines. When the crust is being stretched and pulled apart, there are areas where the rocks are uplifted and form elevated blocks. These blocks are known as horsts.

It is important to note that folding (option 2), mass movement (option 3), and warping (option 4) are not the main processes responsible for the formation of rift valleys and horsts. Folding refers to the bending and crumpling of rock layers, while mass movement refers to the downs