The correct answer is B. Megalopolis
Step-by-step explanation:
A megalopolis is a type of urban area (zone with high density and complex building infrastructures) that comprises different cities or connects two big cities. In this context, the area between Boston and Washington DC is considered as a megalopolis because this area is urban as this area is very developed in terms of buildings and resembles main cities. Moreover, this connects two might cities (Boston and Washington DC.) According to this, the correct answer is B.