Final answer:
The fact among the options provided is that the voting age in the U.S. is 18 years old, as established by the Twenty-Sixth Amendment of the U.S. Constitution in 1971.
Step-by-step explanation:
Among the options provided, A) The voting age in the U.S. is 18 years old is a fact. This is established by the Twenty-Sixth Amendment of the United States Constitution, which was ratified in 1971. Prior to this amendment, most states required citizens to be at least 21 years of age to vote in national elections. The activism of young people, particularly college students during the 1960s, was a significant force behind this change. Their argument was substantially rooted in the principle that if they were old enough to be drafted for military service, as was the case during the Vietnam War, they should also be entrusted with the right to vote.
The push to lower the voting age was also fueled by a broader recognition that young adults are capable of making informed decisions and should have the opportunity to shape the policies and elect the leaders that govern their lives. While some countries have further lowered the voting age, such as Austria and Brazil, where young people can vote at 16, the uniform voting age across the United States remains at 18.