Which practice was abolished by the 26th Amendment?

The 26th Amendment to the United States Constitution, ratified in 1971, specifically addresses voting rights by lowering the voting age to 18. This amendment was a response to the significant disenfranchisement of younger citizens, particularly during the Vietnam War, when individuals aged 18 and older were subject to military conscription yet lacked the right to vote. By abolishing the disenfranchisement of citizens aged 18 and older, the 26th Amendment ensured that this group could participate in elections, affirming their rights as full citizens capable of influencing the democratic process.

The other options, while related to voting and civic rights, do not correspond to the specific provisions of the 26th Amendment. Indefinite detention without trial and mandatory military service involve legal and military matters rather than voting rights. Poll taxes were abolished by the 24th Amendment, which aimed to remove economic barriers to voting, but this is unrelated to the 26th Amendment's focus on age-related disenfranchisement.