Many boston were leveled, and their land was used to fill marshes and wetlands.
a.
hills
b.
mountains
c.
valleys
d.
plateaus

Many Boston hills were leveled, and their land was used to fill marshes and wetlands.

Explanation:

The proximity of the city of Boston to the sea made it vulnerable to the spread of marshes and wetlands. This left a vast amount of land unused and caused great losses on many fronts. To tackle this problem of lands turning into wetlands and marshes, the Massachusetts administration decided to extract earth materials from the hills nearby to fill these wetlands and marshes. Thus, the hills were cleared and the obtained material was used as a filling to cover the problematic wetlands and marshes.