Final answer:
The precipitation and terrain are the features of the Northeast region that keep its rivers flowing swiftly.
Step-by-step explanation:
The features of the Northeast region that keep its rivers flowing swiftly are its precipitation and terrain. The Northeast region receives a significant amount of rainfall, which replenishes the rivers and maintains their flow. Additionally, the region has a varied terrain, with steep slopes and mountains, which help to create a fast and continuous flow of water in the rivers.
Learn more about Northeast region rivers flowing swiftly