Last Year a Pair of Jeans Had a Price of $20

Multiple Choice

Last year a pair of jeans had a price of $20 and this year the price is $25. Which of the following expresses this price change accurately?

A) If this year is the base year, the index number for last year would be 120.
B) If last year is the base year, the index number for this year would be 120.
C) If this year is the base year, the index number for last year would be 80.
D) If last year is the base year, the index number for this year would be 80.