Final answer:
Rock salt mining in the Great Lakes region indicates the area was once submerged underwater, likely due to ancient seas or saline lakes that have dried up.
Step-by-step explanation:
The presence of rock salt mined throughout the Great Lakes region suggests that the past climate of the area was one that allowed for large bodies of water to evaporate, leaving behind salt deposits.
This indicates that the region was once submerged underwater, which would be answer option b). Rock salt formations typically result from ancient seas or saline lakes that have dried up over geological time periods. The process requires a body of water to have a high salt content, for the climate to be warm enough to allow for significant evaporation, and for the area to have limited freshwater input to prevent dilution.