The correct answer is A. On top of.
Recent sediment is deposited on top of older sediment. This is because sedimentation is a process where new sediments are continuously added to the top of existing layers of sediment. As new sediment accumulates, it buries and compresses the older sediment below it. Over time, this process leads to the formation of sedimentary rock layers with the oldest layers at the bottom and the youngest layers at the top, known as the principle of superposition. Thus, recent sediment is always found on top of older sediment.
~~~Harsha~~~