Final answer:
Water drainage in the Great Lakes area after glacier melt followed an easterly direction due to isostatic adjustments, which is the Earth's crust rebounding after being compressed by glacial weight.
Step-by-step explanation:
The direction of water drainage in the Great Lakes area after the glaciers melted is largely due to isostatic adjustments. After the heavy weight of the glaciers was removed, the Earth's crust began to rebound and rise. This isostatic rebound occurred because the mantle material flows slowly in response to the removal of the ice, causing the surface to rise and tilt in various directions over thousands of years. Thus, the correct answer is: d. East, due to isostatic adjustments.