Why did the Great Migration continue into the 1920s?

When conducting research for forming a hypothesis, which practice should historians follow?

How were the okanogan highlands formed? a. by subduction, which caused huge folds in earths surface b. as a result of retreating glaciers carving great valleys into the earth c. when molten rock from under the earth approached the surface d. when the collision of volcanic island chains and ocean rocks formed new earth

What were some reasons the russian people grew to oppose world war i? check all that apply. millions had been killed. food and supplies were running out. the tsar had been overthrown. soldiers were forced to fight. industrialization was happening too quickly.