Answer: D. Twenty-sixth Amendment
Step-by-step explanation:
The Vietnam war brought with it the military draft where young men between the ages of 18 and 21 were conscripted into the U.S. Army.
Proponents of lowering the voting age from 21 to 18, seized on this requirement by the army to say that if a person could go to war at the age of 18, they should be able to vote at the same age.
Congress therefore passed a Bill that lowered the federal voting age to 18 and proposed the Twenty-Sixth Amendment when the Supreme Court ruled that Congress could not force States to abide by the federal voting age.