Although Many Areas of the Continental Shelves Are Relatively Featureless

Although many areas of the continental shelves are relatively featureless, there are some locations on the shelves that have received extensive glacial deposits and significant dissection by streams.How would this have been possible?

A) Glaciers and streams were powerful enough to shape the shelf underwater.
B) The shelves were once above sea level but have since dropped below sea level due to tectonic activity.
C) The sea level dropped during the last glacial episode because water was stored in large ice sheets, exposing the shelves.
D) As the continents collided in the past, the shelves were lifted above sea level and became exposed to the elements.