How did the United States acquire the area labeled number 4 on the map?
A. Mexico sold the territory to the U.S. in the Gadsden Purchase.
B. Mexico ceded the territory to the U.S. after the Mexican-American War.
C. The U.S. purchased Texas from Great Britain after the War of 1812.
D. The U.S. annexed Texas several years after it had gained its independence from Mexico.