Which of the following was not a modern (after 1920) modification to Boston’s environment?

Mill Pond and Back Bay were filled in during the 19th century, before 1920, as Boston expanded its land area. The other choices describe later projects: Logan Airport was built on filled land, and the Big Dig rerouted highway traffic underground. Therefore, the filling of Mill Pond and Back Bay was not a modern modification after 1920.

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