Note the Map Below of the Western United States

Note the map below of the western United States. The dark lake is the Great Salt Lake and is the only lake still existing today. During the last ice ago a lighter blue areas were there too. Why are they no longer there?

A) The weather today is warmer and dryer.
B) The glaciers were sitting just below the surface of the rock under the lakes, and have now sunk to depths of 100 km.
C) The ocean used to flow into the continent's interior and now no longer does so.
D) There was a large ice dam during the ice age that broke and released the water.