Answer: a. The Law of Lateral Continuity
Step-by-step explanation:
The law of lateral continuity is used to explain that the rock layers of the Grand Canyon and indeed other layers of sediment originally used to be wider across and extended continually and laterally across the landscape.
They are now narrower now however, due to the millions of years of erosion that affected them such that now they are separated by various features such as valleys that were caused by the aforementioned erosion.