Nina is researching a biome that has warm, humid summers; cold, long, and snowy winters; and at least four to six frost-free months each year. which region is nina studying?

The biome described is the Deciduous Forest 

This biome is is located in the mild temperature zone, and its major regions are located in Eastern North America, Europe and Eastern Asia.
Other characteristics of this biome include the shedding of leaves of trees, and the presence of four seasons. The leaves are shed in fall and grow back in spring.