The correct answer is D) lowered the voting age to eighteen.
Before this constitutional amendment, the voting age was twenty one. This change in voting age was prompted by several different factors including:
1) The amount of people under 21 who served in Vietnam- Thousands of young men under 21 were drafted into the military to fight in Vietnam. However, many felt it was unfair that all these men had to serve without the right to vote for the people sending them overseas.
2) Protests on college campuses- There was widespread anti-war protests on college campuses. These prompted students to demand the voting age to be changed, as they felt it was unfair that they had no voice in the political process.