The atlantic ocean and the great lakes have different elevations. which two human made structures ships navigate through the sea way?

Locks and Canals

Explanation:

The Atlantic Ocean and the Great lakes have different elevations because of canals and locks that help in bringing ships to navigate through the seaway. The canal is human-made waterways that permit ships from both sides to enter and reduces the time of journey. The locks in canals help in altering the level of water of the canal by filling it up or decreasing it.

a characteristic is a deep cut in the earth or left over rock aka till.