1. Historically, the MOST significant geographic obstacle to the western migration of people from the east coast of the United States during the 19th century was
A) the Great Plains.
B) the Rocky Mountains.
C) the Mississippi River.
D) the Appalachian Mountains.

2.Which age group accounted for approximately 20 million males in the year 2000?
A) Age 0-4
B) Age 5-19
C) Age 20-29
D) Age 30-44

3.The Dust Bowl was one of the largest ecological disasters in World History. In the 1930s, storms of dirt and dust raged across part so the midwestern and southwestern United States. By 1940, 2,500,000 people had moved out of the states in the Great Plains. Roughly 10% of those people moved to California in hopes of finding jobs.
From the excerpt, you can determine that for people living in the Great Plains, the Dust Bowl would be considered a
A) push factor.
B) pull factor.
C) coastal front.
D) maritime tragedy.