Explanation:

- Option 1: In 2004

- 2004 is not the year when the voting age was reduced in India. It was a year of general elections, but the voting age had already been lowered by then.

- Option 2: In 1998

- By 1998, the voting age had already been reduced. This year is notable for elections but not related to changing the voting age.

- Option 3: In 1991

- Although a significant year in Indian politics, the voting age had been reduced before this year.

- Option 4: In 1989

- The 61st Amendment Act was enacted in December 1988, taking effect in 1989, which reduced the voting age from 21 to 18 years.

Option 4 is correct. THE VOTING AGE WAS REDUCED TO 18 IN 1989. .