Rift valleys can form when fractures in Earth's crust widen. The valley walls slowly move at a rate of only a few millimeters a year. Which of these best describes the type of tectonic activity that forms rift valleys? A. Rift valleys form where a continental plate moves under an oceanic plate.
B .Rift valleys from where a plate slides horizontally past another plate.
C. Rift valleys form where two plates move away from each other.
D. Rift valleys form where an oceanic plate moves under another oceanic plate.