The Great Lakes of North America Were Created by

The Great Lakes of North America were created by

A) continental glaciers that carved deep into pre-existing river valleys,creating troughs,which filled with water.
B) continental glaciers,which deposited ice in till plains.
C) cirque glaciers.
D) isostatic subsidence of the crust.
E) millions of cycles of freezing and thawing that broke down the rock that was carried away by flowing water.