In 1990,Professor Fellswoop Made $12,000,in 2000 He Earned $24,000,and in 2015

In 1990,Professor Fellswoop made $12,000,in 2000 he earned $24,000,and in 2015 he earned $36,000.If the CPI was 40 in 1990,60 in 2000,and 100 in 2015,then in real terms,when was Professor Fellswoop's salary highest and lowest?

A) highest in 1990; lowest in 2000
B) highest in 2015; lowest in 2000
C) highest in 2000; lowest in 1990
D) highest in 2015; lowest in 1990