Although sea-level falls can be tied to tectonic activity, they most commonly are tied directly to growth of A. new species B. ice sheets C. volcanic activity

The phenomenon of sea-level falls is indeed most commonly associated with the growth of ice sheets. When ice sheets expand due to climatic changes, water is stored as ice on land, leading to a decrease in ocean water volume and consequently causing sea levels to fall. This is especially evident during glacial periods when large ice sheets cover significant portions of the Earth's landmasses.

While tectonic activity can affect sea levels by altering the shape of ocean basins or causing land uplift, the primary driver for recent historical sea-level changes, particularly in the context of the last few glacial and interglacial cycles, is the accumulation of ice on land.

Final Answer: B. ice sheets