The correct answer is: C. boomer
Explanation:
1. Oklahoma was the first state to enter the Union as a "boomer."
2. The term "boomer" refers to those who participated in the Land Run of 1889 in Oklahoma, where settlers raced to stake their claims on available land.
3. These settlers were called "boomers" in contrast to the "sooners," who illegally entered the territory before the official start of the land rush.
4. Therefore, Oklahoma's unique entry into the Union as a "boomer" distinguishes it from other states.
