A divergent plate boundary is where two tectonic plates move away from one another, so because of that a few options can be dismissed.
Rugged mountain ranges happen two or more plates converge.
Earthquakes happen when two plates slide past one another.
Hot spots are assumed to happen when an area of low pressure appears in the mantle, but that has not been proven.
That leaves us with deep-sea ridges. Deep-sea ridges tend to form because the plates subduct under continental plates, pulling the plate apart and forming a deep-sea ridge.