Final answer:
A sea stack and a spit are both formed by the erosional and depositional processes of waves and currents in coastal areas.
Step-by-step explanation:
A sea stack is a vertical column of rock that is isolated from the mainland, formed by the erosion of sea waves on a headland. A spit, on the other hand, is a long narrow landform that extends out into the water, formed by the deposition of sediments carried by longshore drift. The similarity between a sea stack and a spit is that they are both formed by the erosional and depositional processes of waves and currents in coastal areas.