Which geological feature forms as a result of tectonic plates diverging?

The formation of a rift valley occurs when tectonic plates diverge, or move away from each other. This divergence can happen in continental regions and is often associated with tectonic activity that leads to the stretching and thinning of the Earth's crust. As the plates pull apart, the central part of the crust can sag or subsist, resulting in a valley-like structure known as a rift valley.

In contrast, a subduction trench forms when one tectonic plate is forced beneath another, typically at oceanic-continental convergent boundaries. Mountain ranges are generally formed at convergent boundaries where two continental plates collide, leading to the uplift of land. A transform fault, on the other hand, occurs where tectonic plates slide past each other horizontally, causing shear stress, but does not result in the formation of a rift valley. Therefore, rift valleys are specifically associated with the divergent motion of tectonic plates, making it the correct choice in this context.