Question

Which is the best definition of the word "naturalization"? A. the ceremony performed to welcome a new president B. the process of jury selection used in the court system C. the act displaying patriotism to one's country D. the process of becoming a citizen of a country

Answer 1

D. The process of becoming a citizen in a country 

It's because the definition of "naturalization"  would mean the admittance of a foreigner to the citizenship of a country.

Ex.
"an application for naturalization as a american citizen"

Answer 2

The answer is the process of becoming a citizen of a country.